Honestly, I don't think you're pregnant. Basically everyone has 'clots' when they get their period. It's more than likely old blood. Plus your boyfriend(or ex now?) used a condom so you did use a form of protection. It's not 100% foolproof but it's something. It's safer than nothing. Period blood can be a variety of different colours(of red that is) and you can also have a variety of discharge.
Is this the only symptom you have?
Ultimately, the only way to find out would be to take a test, or wait for a while to see if anything develops. However, I would advise you not to do anything stupid at home. There is no safe way to abort a fetus in a home setting. If you do wind up pregnant, please do tell your parents instead of endangering yourself. Trust me, pregnancy doesn't mean the end of the world.
Best of Luck!