Hi there.
First, congrats on passing (part time) and for already using the men's restrooms as a pre-T FTM! That's quite an achievement IMO. I have not yet experienced the passing issue with public bathrooms since I am not able to pass so I only use the women's restrooms. I have some suggestions that you might want to consider. I see your situation as a transgender rights issue. You need to use the appropriate bathroom that matches your adopted gender, which is male. Do not worry about the fact you are in the early stages of transition; this should not matter because you identify as trans and are presenting yourself full-time as male. So, for you own personal safety and peace of mind, e, set up a meeting with an on-campus faculty member to discuss your concerns. This meeting should be done as soon as possible and in person, face to face. You want this person to see you. Tell this person your situation and your concerns for safety and protection in their bathrooms as well as anywhere on campus. You need to find out the school's attitudes on transgendered students. The point of the meeting is to, #1, make them aware they have transgendered students, #2 safety and security is a grave concern to trans people due to the fact that crime and discrimination is high in our group. The school is responsible for the safety and security of ALL students. Do not allow the counsellor to tell you which bathroom to use; this is YOUR choice. It is your right to use the bathroom that matches your identity, which is male. The school needs to accommodate your needs and this includes the bathroom.
Also, you need to find as much support as you can. Does this campus have a club or support group that includes trans people? A GLBT group? Join it! Even if you find you are their only trans member, it gets you connected with the community and who knows, maybe you will meet others who are in the same or similar situation as you.
Good luck to you!
Miles