Why am I doing this?

I'm new posting on here but don't know what to think about this. I am an 18 year old female who was diagnosed almost a year ago with Homosexual Obsessive Compulsive Disorder. It all started probably around my freshman year of highschool when a pal of mine kept persisting that since I wasn't moving any further with this guy I was interested in that I was secretly homosexual. When he sId this my skin got cold, my stomach dropped, at the idea. I didn't like it, it upset me a bit but I told him that wasn't true. Ever since that day I couldn't stop thinking about it. I asked my dad about it and he says not listen to that guy. After that I relaxed a bit but every day after I couldn't just drop it. I started question if I thought of my female friends as more than just friends. I couldn't look at some of them without getting is urge to do something sexual to them and tried to avoid eye contact because I was terrified about it. I started yo surround myself around more of my guy friends to assure myself that I was and am straight. During breaks from school I'd get depressed, couldn't close my eyes to rest without seeing homosexual images (Even now I'm scared to go to sleep and try to stay up as late as possible.) It wasn't long before I was advised to seek a therapist. i have been seeing a therapist for a while now and have been put through the process of "desensitization".

The problem when I started this was when I began getting groinal responses to images of females and that freaked me out even more. Lately I try to ignore it and have been to look at other females without getting some image in my head. Sometimes though I have bad days and can't. I don't want to like girls but I feel stuck with my progress on handling this HOCD. Recently I can't think properly at al, whenever I am not paying much attention to my thoughts I get homosexual one and when I realize what thought, I try to shut it away with a straight thought. Now though, I find myself constantly doing little checks, I repeat that I don't like the same gender just to make sure I don't think something homosexual. Sometimes out of the blue though in my head I think the opposite and it bothers me so much. I'm so confused because when I say I don't like girls, my head makes think as though I that wasn't so. But I can't suddenly want to like girls but I don't. I feel like I'm helping fuel my HOCD.

I have low self esteem, I haven't had any sexual experience and I don't understand why I'm acting like this. I don't feel like myself anymore.