We've been over run with mossies this year so massive sympathy from me. I've had cellulitis from a bite and I can't sleep if I hear them in the bedroom!
They were breeding in a drained pond with about two inches of water in a small corner right at the bottom (so no fish in there).
A small squirt (literally a few drops) of washing up liquid got rid of them as it stops them laying eggs as it sits on the top the water. Obviously you cannot do this if you have a pond with fish etc, but we researched it and it doesn't bother frogs (we still have lots of those and they have another pond they use).
So, if you have standing water in your garden, tip it out (so buckets, pots etc) as that is where they will breed.
Skin So Soft is great as is Vaseline moisture spray. You just need to make your skin oily as they stick to it and they don't like it.
Repellent with DEET is good as well (but do not get it on your face, particularly your lips). Jungle Formula is one I've used but some cheaper ones contain DEET.
DEET will also work to prevent flea bites.
If the bites are mainly around your ankles and legs, and you're usually covered up or don't go in the garden in the evening or have your window open, then it's possible it's fleas.
When mossies bite in the night it's usually on skin they can get to easily - so unless you're naked without a cover on you would usually be bitten on your back, shoulders, arms and face.
If you think it may be fleas, then you might want to fleabomb the house as they will come home with you on your clothes.