Help please!

My wife & I have been ttc for 2 months. I started taking prenatal vitamins before trying. Got my period December 1 & was intimate on December 14. I got my period round Christmas eve, but was lighter & only lasted 2 days. Took 7 tests & went to the er, all negative. Got another period January 26 & lasted 2 days & was much lighter. My periods have always been normal. My boobs & nipples have gotten bigger & my stomach feels hard. Could I still be pregnant? Has anyone else ever had this happen & turned out to still be pregnant? ??