When did I conceive?

I wanted to know if anyone has a possibility when i may have conceived i got positive results today from home test an at doctors office july 19th from my knowledge I thought i got a period 7days ago but according today the doctor says my period from last month was my actual last period which was jun 17th she said that made me four weeks but is it 4 weeks in some days me an my partner had sex jun 22nd two days before my menstrual ended personal but we always had menstrual sex made my cramps better i went to the doctor she says im pregnant about 4weeks