Pregant maybe or just crazy

Ok so my period was suppose to start November 16th but it was 5days late. usually its always on time but this time it was late i thought i was pregnant but me and my boyfriend had sex on the 5th day and my period came within a couple hours. My period started on November 21th and end November 25th. it was not normal, usually my period last 7days  but this one only lasted 4. kinda strange, My boyfriend and i had sex on the 28th. which is when i was suppose to be fertile if my period came on time. So because my period was 5days late does that change my fertile and ovulation days? Idk what to do, i just started tracking my periods so im new to this, i am 19 years old and i already have one 3year son. (YES I KNOW USE PROTECTION) anyways please help with some advice. :(