Thanks for the query,
If her last menses were on 28th Jan and you both had unprotected intercourse on 15th Feb, then for sure she was in her fertile period if her menses had been regular earlier. the chances of pregnancy are increased if intercourse occurs in fertile period, hence it is important now that she has missed her menses by more than 2 weeks, a urine pregnancy test must be done to rule out pregnancy first. She may be pregnant.
Hope this helps.
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