could i be pregnant!!!!????

I am on the depo and got the first shot in feb. Ive been on it before so i know how My body reacts. I was on antibiotics and had unprotected sex twice last weekend on Sunday with My bf. I am not supposed to have My period until the last week in April or the first week in may. Ive had some náusea, back aches, and tenderness on My abdomen. Since the end of the dayy yesterday, ive had some pinkish discharge. Like a very light period, and im thinkin it could be the implantation bleeding. Idk. And I want to take a test asap just so i can be sure. When can i do that? Could I be pregnant?