What Causes Irregular Periods?

Hello. I m worried about my period.. I started my period when I was 12 (I m 19 now) and it was kind of regular. But slowly, I would mis my period for a month, then get it the next, then miss two months, then get it, then miss three months, and so on.. then I started missing my period for maybe 6 months, then getting it for 6 months straight. I ve been on my period since last November, and it is currently October, so almost a whole year! It s always been light, so I didn t worry too much. But it has got heavier lately, and last week, I started getting blood clots. I ve had this before, but for maybe a four to five days....? But I ve had this for 8 days now, and the clots have gor bigger, ranging from the size of a quarter, to the size of maybe four quarters put together. My period has also got a lot heavier, and I have to change my pad at least once every two hours....? It is not as bad during the night, but I have to put on a new pad before I go to sleep, and then change it as soon as I wake up in the morning. I recently lost about 15 pounds within two weeks, so I know the sudden change in weight may affect my period I know I should go to a doctor, but I m still a virgin, and I m really nervous and scared about the doctor having to look down there.... I feel really uncomfortable about it, but I m also very scared about there being something wrong with me. what should I do?