"Chemical pregnancy", in pain again, very confused...?

A little over 2 weeks ago, my period had been a week late, I'd been having some funny symptoms, so I took a HPT at night that had a very clear "plus". The next morning, I woke up in a bed full of blood (very very heavy bleeding) and crippling abdominal pain. My husband wanted to take me to the hospital right then and there, but I refused for 3 more days. Finally, I went because the pain wasn't ceasing. At the hospital, they took blood and urine, did an internal exam/pap smear, gave me a external and internal ultrasound, and did a cat scan. Not only did the doctor say they could find nothing wrong, but that I was in fact in excellent health. The only idea he had was I may have experienced a "chemical" pregnancy, which is basically a very very early miscarriage some women can just mistake for a regular period, and all signs of me ever being pregnant would have been gone by the time they ran tests. The pain did eventually subside, and I felt fine last week. Yesterday though, I woke up and my breasts were very sore (I don't actually ever remember them being sore at all, ever, before, I don't get pms bad or anything), and the pain came back as I was walking to work. No bleeding this time though. I have had ovarian cysts rupture and cause similar pain before, but they found no cysts or residual fluid of a ruptured cyst when I was at the hospital, and I seriously doubt one could have grown big enough to rupture and cause immense pain in under 2 weeks. Even if it's hiding from the tests, I just know something is going wrong in my body. The pain is in the lowest part of my abdomen, and it's actually tender to touch. Since I don't feel it's an emergency, and the hospital couldn't help last time, I will be seeing my regular doctor this time. I'm just not understanding what is happening. I'm just looking for some ideas of what might be going on, so I can ask my doctor to test and eliminate it as a possibility or find what's wrong. Anyone else ever experience things like this? I'm 99.99999% sure it has something to do with my female parts malfunctioning, but past cysts or pregnancy, which have been eliminated as causes, I'm not sure what else it could be? And before anyone says it, I DO NOT have a STD (which much to my embarrassment, they routinely test for at the hospital, making me feel like a complete idiot in front of my husband).