As long as you don't continue to take midol it shouldn't really hurt the baby in my opinion. There are a lot of women that unfortunately don't know they are pregnant, and they will still drink alcohol or take other medications and have healthy babies. As long as you stop now, there should not be too big of a problem.
However, I wouldn't even worry about it until you test!

If you are at the point where its your missed period, I would go get a test and take it tomorrow with your first morning urine. If you had unprotected sex, there is always a possibility of pregnancy. Have you been using protection?