possible pregnancy?

So I had a period last month I had 2 periods, I had one at the beginning of the month then one 2 weeks after I had sex, so since I had the second period it's been 2 weeks since I had my last period.. ive gotten crazy acne ,period like cramps,have had nausea 3 days in a row now,back pain sometimes & I've been having an appetite and cravings ,should I take a pregnancy test I don't think I'm pregnant becaus the period I had after sex was normal kind of and I've been having heartburn

what should I do BTW IM 18