I've had frequent head aches and a dizzy feeling now for 6 days. Could it be because I've recently had a miscarrige.?

Maybe. Headaches and dizziness can result from many different things, from dehydration or lack of sleep to bleeding, among others. If you are continuing to have a lot of bleeding (greater than 1 pad/hour), you should go to your local er to be evaluated. Otherwise, make sure you are taking care of yourself (i.e., eating well, sleeping well), and follow up with your doctor if you continue to have the pain.
Depends . There are a variety of possible reasons for the symptoms you are having, with sinus congestion high on my list. If you had an uncomplicated miscarriage and are having no abdominal or pelvic side effects they are not likely related but without a lot more clinical information its impossible to rule that out completely. Call your doctor's office and ask to speak to their nurse.
See your doctor. You need to see your doctor right away to check for problems related to the miscarriage.