What should i do?

My periods have been getting shorter and shorter. They started getting really weird off schedule, lasting forever, getting shorter and lighter, now im down to basically a 2 day period. Im only 18 and i dont know whats going on. And ive gotten what seems to be a really bad yeast infection or something that hasnt gone away with monistat. Its been 3 weeks since my symptoms started. Ive only had one yeast infection before and i was 11. Could that be effecting my period?