While I can't tell you whether you are ftm or not, I can offer you some personal experience.
It might seem like it, but not everyone is 100% certain their entire life. For the longest time, I had no idea. I was just me, and didn't question anything. I accepted that I was a "girl". However, now that I look back, there were lots of "pointers" there, right from the beginning. Since I had no knowledge of what trans was, I figured I was just a "girl" who liked not so "girly" things. I suppose here's where your typical story begins; I used to hate dolls, liked car toys and all that, not going to type it all out. Either way, my point is, I didn't really know for a long time. And I couldn't possibly be the only person.
Moving on to a timeline closer to when I realized, I used to often go around filling in my "gender" on the internet as "choose not to state" or hide it from the profile. Eventually, I refused, whatsoever, to tell people what "gender" I was. Later on, a lot of times, I would play mind games with people and make them confused (I used to do this with a lot of other things too though), and eventually they would generally think I was a guy. That idea pleased me, and I really liked it when they would refer to me as he/him and all. (Might be a good idea to try that for yourself, excluding the mind games part. Just "try" being male on the internet for a while and see how you like it.) Later on, I started playing online games where I always had a male character. People assumed I was a (cis) male and treated me that way. I felt pleased with that as well, although sometimes I felt a little guilt for "not telling them". Apparently this happens a lot for trans people, so I guess it's normal.
At some point, I had come across the term "transgender". By then, I already knew what it meant, and I had some basic understanding, but for some reason, I suddenly took notice of the word, and even though I was afraid of it, I knew, in the back of my mind, that that was me. For a while, I ignored it. As I said, I was scared of it. Scared of what would happen if I started identifying as trans, as ftm. I would be different from other people, and due to some things that happened in the past, I was scared of being different. I didn't want to be different, so I ignored it. As time went on, I started realizing I shouldn't have. Nothing (in my opinion) particularly bad happened from ignoring it, but neither did anything good. Once I finally started accepting it, I first thought of myself as some form of genderfluid or something similar, leaning more towards female. Though as time went on, I started discarding that and shifting towards something more male. In the end, I ended up with ftm. I kept it to myself for a while, doubting myself (which i still do) and thinking that maybe I really just was cis after all, and that it was all a mistake or a phase.
Around the same time, I sat down and thought for a while. I looked back at my childhood, how I felt, how I acted, all of that, and realized that maybe I really wasn't cis. My entire life, I had felt more masculine, and didn't really like being feminine. It had gotten more intense the few years before I came out to myself. Looking back, I realized that in those few years before, I actually did have some sort of dysphoria. Other than certain designated moments (I'll get into this later), I didn't like being seen as feminine, and I avoided it. While mild, it was still sort of dysphoria.
Thinking of being "seen" as feminine, this brings me to physical looks. With long hair, I look extremely feminine. When I see older pictures of myself, I can't help thinking the girl I see is very feminine and cute. Narcissistic in a way, I suppose, but I don't really see myself in those pictures. I see a girl that is not me (one I would probably consider way out of my league, to be honest). But when I think back at how I felt at that time, I felt masculine, very much so. Yet because everyone saw a petite, feminine me, they treated me like that too, and I was forced to, in a way, think of myself that way too. A bit contradicting is the fact that I, at the same time, thought of myself as very masculine. I remember one time giving advice to a friend who was at the time crossdressing, "You probably shouldn't stand with your legs so wide apart, it's something men do and you'll probably pass better if you don't do it" (Might sound harsh, but he didn't take it that way.) I was met with a response, "But you're doing the same thing yourself!" I suppose it's slightly unrelated, but it reminded me of that.
Now, back to the "designated moments" I said I'd get into later, specifically, this would be dressing feminine, with the intention to look like a female. I'm not entirely sure whether you would call this crossdressing since I identify as male, or not crossdressing, since my body is physically female, but that's not important here. I have a sort of thing for it, always have. At first, I thought this meant I was cis, or at least some sort of female being, but I later on realized that I only see it as a hobby, not something I identify with. In other words, even if you like feminine things, or even dressing up as a woman, it does not necessarily mean you are one.
Either way, this got horribly long and I'm so sorry about that, but I hope you'll read it and find at least some information that will help you.
