My period is four days late. i have not had sex, but i do partake in sexual activity. me and my partner only use condoms for some things, but not all the time. i am not on birth control. should i be worried?

Some normally regular women skip a cycle or two occasionally. In theory it represents lack of an egg release. Delay due to pregnancy would turn a urine pregnancy test positive eventually, though these can be falsely negative early on. If it continues after 90 days some OBGYNs would offer other hormonals to trigger a cycle.

Assuming you do not want a baby at this time, the answer probably is yes: you should be worried about being or getting pregnant. Of course it depends on what you mean by "not had sex" but "still partake in sexual activity"; and for which "things" (sexual practices) you use condoms. I suggest you stop screwing around (pun intended) and get onto proper contraception. Good luck.