Well, that is really an individual situation. Some live in cultures or families or who practice religion that put a lot of negative feeling toward being gay or bi. Is that you? Since you are writing on an ocd forum, do you have OCD?
Mom has asked a good question, as it sounds like you're suffering insecurity and anxiety, not OCD. So have you been diagnosed with OCD? Asking why humans have thoughts is because that's what humans do. We evolved a brain that does that. So we all have thoughts. Whether those thoughts are interesting or bother us depends on our personalities and on present circumstances. For example, if you've just had a bad break-up, such questions would arise for different reasons than if you haven't. The true answer to whether you're gay or not will come from action, not thoughts. Who you are attracted to and have sex with will determine it. Whether one is bothered by being gay or not, to an extent, in the world of the last few centuries being gay was considered by almost every culture to be an offense against their religion and there was great repression. If you go back a few centuries further, it appears a lot of people were gay or bisexual and it was perfectly accepted. Nowadays it's easier in most places to be gay but still not easy, as it takes a long time for social repression to go away completely and for social norms to change. Which means, anyone who is gay or bi probably has some problems with it even if they're sure. But just having thoughts of being gay or bi is different than being gay or bi. That time will answer for you. But anxiety gets worse over time if you don't face it down, so if it's bothering you enough to interfere with your life you might want to talk to someone who can help you through this. Peace.