very Early Very watery Period

Elizabeth
Okay so I have gotten my period 2 weeks early which I cannot stress enough has never happened! I am ALWAYS 31-33 days in my cycle and this came 10 days early..  it has no clots and is very very watery! I thought it was blood in my urine but in closer inspection it is emanating from my Vagina. I'm just worried because like I said I'm very regular and normally have heavy clot filled periods but when this comes... it feels like I peed myself... I've taken 2 pregnancy tests 2 weeks apart and both were negative but my mother had ver low hcg levels and pregnancy tests didn't show up for her until she was 4 months pregnant!
I have recently lost weight, I feel sick and have sore knees... I'm urinating more than usual and my brests are sore and larger than usual.... 
all in all could be nothing I am going to the doctor this week to get checked out.... if it's not pregnancy it IS something so.... I need to know if anyone has anything similar 
The last time I had sex was 5 weeks ago