im really confused

hey guys i got a queston okay i had a period july 29 and when i got off i had sex on the 8 then i waited for my period but no sign i took a test it came out negative :dry: so still no sign of period and a negitive test so i had sex again on the 13,17,19,22 of september. So heres the question could i be pregnant even though i didnt have a period one month and i had un protected sex if so how am i suppose 2 calculate my dute date ????:S im really confused and thanks so much in advance;)