Quoting Marbles.:" Im in a similar situation, I havent had a period since having DD 7 months ago, and about 3 weeks ago ... [snip!] ... with DD I didnt get a positive test till I was 3 weeks late, and since I have no period to go by I have no idea when to test!"
Well I tested about 2 1/2 weeks after DH and I had sex but will probably do so again in a few more weeks just to be sure if no AF since I do have the tendency to not get a positive right away. I would say test. Or wait for like a month after you last had sex