Help!

Ok, I Have had PCOS since I was 16. I've been on and off metformin since then. I was just recently married in August and was on birth control to regulate my periods. In October we decided to start TTC so I went off the pill. I've been on metformin solidly since August. I had 2 regular periods off birth control. My last period was November 3rd. I have been showing signs of being pregnant, exhaustion, mood swings, swollen and tender breasts, nausea, food sensitivities ect. My husband is completely convinced that I'm pregnant but so far only BFN's. I even went to the doctor last week and the blood test was negative. Anyone know what might be going on? Is it possible to not have a period while on metformin even though I always have?