I've been off the depo-provera shot for about 6 months. i had unprotected sex 6 weeks ago. both tests i took were negative. should i still be concerned?

Yes!!!: Even if your pregnancy tests are negative, you can still catch a sexually transmitted infection via unprotected sex. That's why it's so important to make him wear a condom each & every time. Don't believe anything about pulling before ejaculation either. There're plenty of sperm in pre-ejaculate (pre-cum). Of course, condoms aren't 100% effective, so 2nd form of contraception is advised.