I can get it prescribed at medical there or before I show up to OCS ?
Disclaimer: I didn't go through OCS, but I have gone through several other indoctrination-type training (including at least one with a much less flexible and/or available medical support infrastructure). However, others have already said here that once you get to OCS, you can go to medical and get whatever piece of paper you need to authorize you to pop pills. Given it's Navy medicine, I wouldn't be surprised if what they give you is less effective but requires you to take twice as many pills, but still, at least it's something to help with your lady problems.
I think if you search back, I think there was even someone who said they went to medical to get their birth control prescribed so they didn't have to come off of it.