how soon to test?

Sabrina
We've been trying for a baby for a little while now but I ended up getting my period earlier this month. Well the first time this month we've had unprotected inter course was the 10th and so after. It's been 10 days and I'm lightly spotting blood. ( I'm hoping its implantation) 
How soon can I test? I can't go by my period because they've always been irregular.