I Have Had Nausea And Light Cramping For Six Weeks.

I have had nausea and light cramping for six weeks. My period was early and light the last two months. I had a urine pregnancy test and it was negative and a normal pelvic ultrasound a month ago with my first light period which was mostly brown. I have had horrible headaches. My doctor said my hormone levels were normal but he did not do an hcg since the urine was negative. I have hyperthyroidism and I take levothyroxine. Thyroid levels are normal. I have pulling pinching and sometimes burning feeling in my pelvic area at times also. My cycle is a perfect 28 days and only once had been late but never early. Dr said that there is nothing wrong but I'm still cramping and nauseated.