What Causes Sore Breasts, Light Vaginal Bleeding And Back Pain With Negative Pregnancy Test?

I am 32, have had 2 full term pregnancies, 1 that was successful. My last pregnancy ended Feb 21, 2010 with a still birth. I believe I had a miscarriage the following June, and I had bleeding every 2 weeks for the next 3 months with an ultrasound to make sure things were ok in October. Everything was fine and my doctor said I shouldn't have trouble getting pregnant in November.
I am not on birth control, and we're not preventing a pregnancy. In February I had a faint positive test, then several negative ones. Doctor test was negative. Since then I have been experiencing many symptoms and I wonder if my body is tricking my brain. I have sore breasts, odd cramps, lighter periods, a dull ache in my lower back at times and I have been feeling so bloated and uncomfortable and I have been feeling movements that really feel the same as when I was pregnant. My doctors won't give me an ultrasound because I don't have a positive test...? Any suggestions? Cyst maybe? Could that move?