What's going on?

The cycle before last I completely missed my period (very unusual for me) am in the pill but had taken antibiotics so I took two pregnancy tests which were negative. Went to doctors who said it was probably just one of those things. This past cycle u did get what I assume was my period but it was lighter and shorter than usual. I'm also feeling really tired, really thirsty, really hungry and have what I can only describe as pelvic pain. Anyone got any ideas what's going on please? X