Last month got period on the 21st. this month it came today 15 n its brown instead if red. is this normal last time i had sex was 3 wks ago condoms)?

Probably normal: There is some normal variation in cycle length. Any thing from 21 days from the start of one to the start of the next to 35 ( or 42 depending on the source) is considered normal. This is largely because son eggs mature faster than others. Most women have their normal range of cycle lengths rather than a set number of days each month. Hope this helps.