can i be pregnant, implantation bleeding?

I had my normal period on July 20th, then on july 27th i had mildy heavy bleeding for about three days. i have sex with my boyfriend frequently, not always protected. my doctor st the time had tested me for pregnancy and it came up negative which lead him to think i just had a hormonal off balance that lead to the bleeding. it is now august 19th and my breasts are swollen, sore, and veins are clearly visible in the areolas. i also have been experiencing discharge and mild nausea. i now think i may be pregnant. could that second bleeding have been implantation bleeding?