Is It Safe To Take Aspirin During Pregnancy?

I have taken aspirin yesterday, because of shoulder pain, and i got light menstrual bleeding. Since my partner and I have been sexually active during ovulation time, I am concerned that I may have been too quick taking aspirin, since there is a small chance of being pregnant. I am 43 so I didn't expect pregnancy, or I would have checked the implications of taking aspirin. What is the best thing to do now? I called my doctor, but they are not on duty today.