?? If I'm pregnant or not

Hi I'm 23 nd I was wondering what's wrong with me my menstration normally come on for 7 days but this month it only stayed on 4 days what could be wrong with me I went to dha Doctor they said everything was fine but I being craving certain stuff and being having lower back pains stomach bloated be feelin sick some mornings and everybody keep asking me is I'm pregnant I say no cause the doctor told I wasn't somebody please help nd yes I had sex on my ov day but my cycle still showed up but didn last long as normal