did you consider bedbugs? they are making a comeback...
I've heard of the bumps merging into one big one before. I suffer from what is pretty nuch chronic hives. I break out into this patch of itchy bumps that only get worse when scratched and as the bumps expand they'll merge with neighboring ones. I used to get them everywhere but they've calmed down somewhat and I usually only break out on my forearms now, mostly right after I've washed vegetables.
If what you have is indeed hives, hives are an allergic reaction to something- food, medicine, atmospheric, animal, etc. I never did figure what I was initially allergic too (I've been to doctors). However, years after I started getting them , I was stung by a bee (my third bee sting) and broke out in hives everywhere (I mean everywhere. i even had then on my face, and I'd never gotten them before). So, I have an allergy to bees as well as whatever initially caused my hives.
What happended with your doctor visit? Is this really from mosquitoes?