How to know who I am?

First off, some context. I'm an 18 year old bisexual kid from the northern Midwest. Beyond a myriad of medical problems, my life is pretty boring. The issue is, I'm not sure what to think of myself. I don't like guys during the day, but almost exclusively get sexually aroused to men at night. During the night, women seem "meh" and not as interesting as guys. I couldn't ever see myself dating a guy, but almost all sexual fantasies involve my own gender. I've been with girls and guys before, (I'm a bottom if that matters!), and I have to say, I'm not sure what to do about myself. After finishing with a guy, I find myself disgusted by the male anatomy and it takes days for my gay to resurface. This problem doesnt happen with girls. I'm asking the gay community to hopefully shed some light on what I am, and why my homosexual tendencies seem to flicker so frequently? Is this normal? Am I just a swinging bisexual? Am I straight, even if I like guys some of the time? Why does my sexuality change with the time of day, and why am I suddenly unattracted to guys after I have one for a night?