My last 3 periods have been really peculiar - I had one for 2 days when usually it's 5 days, then I just had spotting the next month, then I went back on the combined pill and had 1 regular period. I'm now half way through my next cycle of the pill, I missed one day by about 5 hours and now there is this continual brown fluid - it's thinner than blood and I really have no idea whats going on. There has been some yellow discharge when I haven't been on my period. I've been sexually active for over a year and I have had unprotected sex while on the pill but we were both supposedly clean of any STI's - he did cheat on me while we were still together, so an STI of some sort could be a possibility. I've taken multiple pregnancy tests and they have all been negative. I really don't have any idea what's going on, please help!