Could be anything - ovulation bleeding, vaginal irritation, or implantation bleeding (condoms have a failure rate of a few percent). Take a test in about a week.
I agree with Shuga, I'd wait to buy a HPT until you've missed your missed. It is possible that you could be pregnant, condoms are not 100% effective. If you feel that you need to test buy a First Response Early Response test. It claims it can detect pregnancy 5 days before you miss a period. Good luck to you!
Wait until your period is actually due. Dont' waste money on an HPT test until after your period is due. Timing is important. When did you have intercourse? Yes, Condoms do break but Chances of pregnancy are slimmer, but not impossible.