I work in an abortion clinic, and myself have had an abortion.
Usually they say no sex for 3 weeks because the uterine stimulation can cause pain, cramping and bleeding. If you were going to have an infection it would have happened sooner, normally infections happen within the first 72 hours, if they are going to happen.
I had bleeding for 3 days after my abortion, mostly spotting, and then had some bleeding 3-4 weeks later.
It may be related to sexual activity, it could even be a period, possibly.
If you did not start birth control after your abortion, you could have a period sooner rather than later.
Infections are accompanied by a fever, so take your temp. You could also call and see if they can fit you in earlier.