What Causes Pimples On Arms And Legs?

Hi, I am a 25 years old boy. I have got some pimples on my arms and legs, at the begining they were very small, but after 2 weeks some of them desapeared and some became bigger. I showed the case to the doctor and he removed the big pimple from my skin to make a test of it. We are still waiting for the answer of the test, but he said that it might be furuncle and he gave me tetralysal-300mg for three months and he said that you should not go to the sun at all. These red areas are approximately 1 cm and they are not painful and itchy... I'm alittle bit afraid of having cancer instead of furuncle but I'm not sure. Can you please help me?