What Causes Frequent Urination, Nausea And Missed Periods?

Here's my story: My last period was April 5 and lasted until April 9. More than 40 days later and about 7 negative pregnancy tests, I'm getting worried. This is the first time this ever happened to me. Other symptoms: my breasts hurt, I'm urinating more frequently, I occasionally feel nauseous, and I have slight lower abdomen pains every now and then. I would love to go to the doctor but I just lost my health insurance and in the process of trying to get it back. I'm really starting to freak out here. Any idea what could be wrong with me?