As you obviously know both ms and lupus are auto immune disorders and are often mistaken for each other. You do need a definitive diagnosis for this and your doctor should be more on the ball with the info.
The things you speak of i.e. miscarriage, stillbirth and migraine are but a few of the things that 'can' occur with hughes/sticky blood/aps. I think it strange for your doctor not to want to look into this further when you have 'possible' signs of the disorder.
Is he/she in fact a rheumatologist? A GP is not the best person to look into this, they should refer you on to a qualified doctor who can do appropriate testing and put your mind at rest one way or the other.
I would really push for this to be done, especially if you are of the age when you may want to have children. Of course it isn't only having children that is affected, it can cause other problems.
Please push and push and ask questions, be firm - it is after all your right to find and get the best possible treatment you can.
Take care, goldenwings