Had sex over 3 wks ago. no condom, he didnt finish starting to get spotting but i'm due for a period in the next few days. irregular periods pregnant?

Wait a week or two: A urine pregnancy test won't be sensitive until 7-10 days past when your period is due, give it a bit more time before you check a urine pregnancy test

STD risk: Pregnancy can occur even when there is no ejaculation inside. There is pre-ejaculation fluid that contains live sperm. Unprotected sex significantly increases the risk of STD, which can result in irregular periods or unusual symptoms with a period. The spotting you are experiencing may be the beginning of your period, but if this is unusual for you, you should be evaluated for STD.

May be early period: It may be onset of period early, But if the spotting does not follow by period and you miss your period than do a home pregnancy test to find if you are or not pregnant,What do you mean by he did not finish .If you don't want to get pregnant, I will advice you use Condom next time

It sounds like: what you have is premenstrual. You are on your way to get your period. Take a pregnancy test if you miss your period. Nothing else I can tell at this point . You need to wait and see.