Can someone Please tell me whats going on?please!

Hi, I'm Ashley a 17 year old. I wanted to know whats going on with my body. Yes, I'm sexually active& always had unprotected sex. For about 3 months I've been feeling cramps that bothered me, the cramps did not hurt i just knew they were there. Yes I still get my menstrual cycle but sometimes it comes about a week late. But it still comes. Sometimes it would come hard and sometimes it would come where i won't feel it. I have lost weight i went from 130 to 118 pounds, but still feel like i have not changed a bit, i actually feel bigger. I'm hungry all the time now, but sometimes i'd eat a little because i would get nausea's but never have i thrown up. I would eat a little sometimes also because my lower stomach i would get pain. I have a lot of bubbles in my stomach, i get a lot of gas to at times. My Breast don't hurt, only a week before i start my period. When i lay down and someone pushes on my stomach it hurts like it's sorta sensitive I do not have a clue why. I need to get checked by a doctor, but I would like some Opinions first. Thank you.