pregnant again following a miscarriage?

Ladies, it's possible I could be pregnant again right after a miscarriage but I'm not positive. I go to my ob follow up appointment in a couple days and I'll find out then. I miscarried 6 weeks ago with my twins but I chose to give birth to them in the hospital 4 weeks ago. It could be just old hormones but it looks to me like the lines are getting darker. Can women still conceive while postpartum? A couple weeks ago, my boyfriend and I had sex and  ever since then my bleeding stopped until a couple days ago when we had rough sex(it's been a while) and my bleeding came back light. Do you guys think I'm pregnant again? The last test I took was the expensive one and I really wasn't paying attention to the time so I'm not sure if it's an evaporation line, but it looks like it has a pink tint to it.