Menstual cycle becoming infrequent ?

I am a 19 caucasian female, 5'2", 125-130 lbs. My menstual cycle use to come on the 27th every month(religiously since I was 8 years old), was extremely heavy, I had horrible pms (PMDD) preceding it, and it lasted 5-6 days. In december my period started the 20th, was very light I didnt have pms and it was 4 days. In January it came on the 18th lasted 2 days, 1st day very light, 2nd day almost normal, then it stopped. 24 hours later it started again but only spotting which lasted 1-2 days. I am also having frequent urination (It is not a UTI or kidney infection) and I am horribly fatigued all throughout the month and nauseous after eating or smelling certain foods. What is going on with my body?