What's going on?

I know some professionals and quiet a few well informed people use this forum and I was just wondering if anyway had any idea about what is going on with me.

I'm trying to get pregnant again and after some less than normal pregnancies in the past thought you could shed some light on what is going on with me and therefore help me become pregnant.

Ok so my cycles are fairly regular at 28 days and based on that we have been given a due date for my past 3 pregnancies (resulting in 2 miscarriages and 1 stillbirth (1 set of twins)), but when we went for our dating scan the pregnancies where 2 weeks behind the date based on my cycles. My doctor said that I must ovulate late, but if that's true why do I get positive HCG tests at the time of my missed periods?
The only pregnancy that I've had that went to term, the baby was born 2 weeks early, so was that just a coincidence and I really do just ovulate late? Or was that the babies actual due date and for some reason (possible related to my recurrent pregnancy loss) my babies just measure 2 weeks behind in the scans?

Do I ovulate late?

Is this something that I should speak to a specialist about?

I know I will probably never know the real reason for why everything is so weird with me but at least it might be helpful in TTC my next baby if I have some idea especially about when I might ovulate.