Causes of Itchy, Red Rash

I get itchy rashes on my belly, arms, and legs. They look like mosquito bites at first, but after some time, the itch becomes less intense, and the color turns dark, leaving little dark dots on my skin. Sometimes a bit of fluid comes out of them. I have tried different kinds of medicines and ointments, but they never really solve the problem. What can these rashes possibly be? What can I do to get rid of them?