My last period was on the 28/10/2011 my gp say's I'm 7 weeks pregnant now,but how could that be if I ovulated around the 10th nov, last week on the12th dec I had a scan and I was told that I'm 5 weeks yet I don't understand how could that be according to the ovulation date

Weeks pregnant are estimates based on information you give the doctor or from average size of fetus at various levels.
They are often best guess dates give or take a week or two.

Next unless you are tracking your actual fertile dates, they are not the same for everyone, it is possible to get pregnant having sex during your periods at time, he week after, and he week before.

But you are pregnant, so the exact date that you conceived should not really be that much of an issue. Unless there was multiple partners during a couple week period. If of course that is the worry, nothing can determine that till the child is born and there is a DNA test

I did sleep with 1 person on the 5th nov and then I it was my husband on the 8th and so on.. it was a very big mistake that happened at that time.. and the period date was 28/10/2011 so who's should I think it is,I'm so worried I can't even be happy for a second or even tell anyone in the family

I did sleep with someone on the 5th nov and then it was my husband from the 8th and so on.it was a very big mistake and I can't sleep or eat thinking who's it is.I can't even talk to anyone that I know about this because I don't want a divorce,my last period was on the 28/10/2011 I need someone to help me with this

There is no way to tell which person is the father, till you have a DNA test when the child is born.
Legally is you are married, in most areas ( not sure where you are at) but if married the child is considered legally the husbands even if it is not.
Of course it would be perhaps worst to not do a test and for husband to find out 10 years latter the child is not really his when something happens to cause him to find out.