definately a dust mite allergy I'd say. Take an antihistimine before retiring and also as the other posts have said, pull your covers back in the day as the sunlight kills dust mites. Try vacuuming your bed or if you can, purchase a new anti allergy matress. You can also purchase anti allergy covers for pillow and duvets and matresses which go on the items under neath the bed clothes so you don't see them.
Try to cut down on soft furnishings: change the curtains for blinds, maybe take out rugs if you have them and replace the carpet with a hard surface floor eg laminate/floorboard etc.
obviously, you may not be able to do all these things at once, but if the anti histamine works, it would suggest that that is the problem.
it would also be worth seeing your GP as he can prescribe a much stronger antihistimine than over the counter and it is cheaper on prescription as you will probably need it all year round. Also he can arrange allergy testing for you to see if it definately is dust mites.
good luck.