I had sex for the first time about a month ago, and a few days later I noticed that there was some blood on my underwear although I did not bleed during the time I had sex. I am 17 years old and really don't want to be getting into pregnancy. My partner used a condom with spermicide and did not inside, yet I still worry since I thought that the blood a few days after may have been spotting. I haven't had symptoms like nausea or dizziness or swollen breasts, but I feel the need to urinate often, though when I go to the restroom, I don't actually have to use the restroom. My period is regular and starts usually the 19th or 20th of each month. It's the 20th today and my period hasn't started yet. Should I be worried?

Pregnancy is always a possibility. Right now you are playing the waiting game. If you don't have your period in two weeks take a pregnancy test using first morning urine. Follow the directions on the box carefully.

It is normal not to have any signs now, those come a month or so, after you miss your first period. ( although some women may have early signs)

So normally the first sign, is just this, a missed period.

It is possible, that you can be pregnant, ( or perhaps have an infection)

At this point, you and 1000's of women are playing the waiting game, you will have to wait for about another two week, and see if period starts, If not, take a test wit first urine of the morning.