hello, Welcome to HCM. First of all, you did sex 2 weeks before period date i.e. during your fertile period and you have HIGH chance of pregnancy in this context. Above clinical features with missed period and brown spotting are most suggestive of pregnancy. Here, I suggest you to undergo one home pregnancy test at the earliest to clear doubt. In absence of pregnancy, you may need to undergo hormonal profile and USG lower abdomen to rule out other underlying pathology. In early weeks, pregnancy symptoms are nausea, vomiting, abdominal bloating, breast discomfort, headache, tiredness etc. So, consult with your gynecologist after getting test result for next level management. Practice safe sex in future. Take IRON supplements. Good luck. Be well and tc.