The chances of it actually happening to you are extremely low, provided you do not take risks or put yourself in any risky situations at work. I say this as someone with some experience of both pregnancy, and of dealing with people at former work places (and landlords) who were utterly skeevy.
Maintain and be mindful of personal space. If someone gets too close, step away and maintain body language that suggests no interest. You could resort to aggression but in my experience that tends to lead to being fired. For now, I would suggest doing what women do because they are apparently perceiving you as a woman, which is making it clear you are not sexually interested in any of them, and not hanging about on your own in their sight. Skeevers know their actions are not socially acceptable, so they do them when others are not around but you. To avoid this, don't be alone in their presence if at all possible. Call others over, make it evident there are people about to back you up.
Provided you do not appear to "lead any of them on" by being friendly, or making any sort of gesture that would seem you are allowing what they are doing (this can include something as simple as "laughing along with" someone you don't like, or agreeing to have coffee with someone, so be aware) you should have little problem as most men know they are being rejected and it happens to them often enough that they will move on. If you have a truly "desperate" guy friend, be cruel to be kind and make it clear you are not interested, preferably by switching subject, or telling them outright you are not. If they are unstable enough to be a problem in this regard - you'd do well not to have them as friends.
As FTM I have found my own confusion as to how to treat other men who perceived me as a woman took decades to resolve and understand. They will be bemused and frightened by aggression in what appears to be a woman, but not in a way that tends to resolve itself easily. Smiling, laughing, and "pretending" to get along with someone can easily be taken for interest in them, so avoid that. I have a terrible habit of laughing when I am revolted or bemused by something, including a person, and its somewhat uncontrollable - when trying to get rid of an unwanted interest, this isn't the best thing to do because laughter can be seen as an approval or endorsement. If you are truly repelled by someone, then show it, not in an over the top fashion, but make it very clear you do not want to be near them or talking to them any longer than you absolutely have to.
Observe "disengagement" and "deescalation" tactics in women and how they do it without coming off as nasty. Once you transition and begin to be read as male none of this will likely be much of a problem for you any more.