I doubt very much that you have mites from the little that you've told us. Biting mites can only live a couple weeks without a host (that'd be a living blood bearing source, not a fabric stash) and you said you're only bitten in the summer months. One doctor said insect bites (mites are not insects, btw), another said an allergy. You really don't have a good idea of what's causing what you assume are bites.
Ask yourself some questions to try and narrow it down. Do you have pets? Are there mice in your house or nesting nearby? Are other members of your family suffering the same skin irritation? Does it only happen in your sewing area? Do you have to come in direct contact with the fabric to have the irritation occur? Do you open the windows in the summer? Does dust and pollen blow in? Do you have any known allergies? Sensitive skin issues? If your doctors didn't ask things like that, they should have. Don't just assume mites are the cause...it could easily prevent you from finding a real solution.