Help!!!!

Ok, Ben trying to get pregnant for over a year. For two weeks now my breasts/nipples have been sore (even to wear a bra), nauseated, had acid reflux (never had before).. Well my period was 6 days late today. Took four pregnancy tests yesterday and the day before. All of which initially said negative but hours later were positive. Well then this afternoon I had a little blood in my underwear. It's still very light (haven't had to change my pad once).. I normally am very regular, every 28 AND have heavy periods.. Still having all the symptoms. Please help!! My son is 3 I don't remember what it's like.. Could I still be pregnant? Could it be implantation bleeding? (It has been exactly 12 days since one of the days we had intercourse)..