Hello my last period last month ended in 13, and we have have sex with my husband. But after a few days I felt that I am pregnant I took a pregnancy test after 3 weeks during night its positve two lines came out. But I wondered if I this true because my period is irregular I mean sometimes it will come on the first week, or second week of the month or last week of that month.

Much too early to get any sort of meaningful result.
You must wait till your expected cycle is late, by about a week for a true result with FIRST morning urine.

If your Sept period ended on the 13th the, its too soon to take a test, especially if you don't follow instructions.

Wait until the end of Oct.

Agreed, while a false period is seldom, the issue is you need to test in the morning, and need to be at least two week late to period.