I'VE NOT SEEN MY PERIOD FOR ALMOST 7 WEEKS NOW, YET I'M NOT PREGNANT 

I've Not Seen My Period For Almost 7weeks Now, Yet I'm Not Pregnant 

I am confuse, needs advice on what step to take next.

The whole thing begins on 25th July when i had unprotected sex with my bf. before then my last period came on the 17th of July.

 so i had sex just about a week after.

Since then uptil now i have not seen my period. 

Initially I worried i may be pregnant but after several urine and blood test it all turns out negetive. 

what could be wrong here? 

This is the first time i am experiencing this.

I have done 4 test myself using pt test strips. but all came negative. Yesterday I went to a private lab an de used my blood and urine sample for pregnancy test, it still came out negative.

Abeg any medical expert or any one with past experience should assist with advice on next step please.

Note, my boyfriend is aware of the whole situation. he himself is confused.

 I am 23 yrs old just incase 

thanks