Suggest Treatment For Sore Lumps On Top And Back Of Head

Hello, for over a year now I have been getting sore lumps on the top and back of my head. They are mostly smaller like a large pimple but without a head and when they pop a clear liquid and little blood comes out, some of them however grow quite large and painful and then these ones pop large amounts of greenish puss and blood emerge. I have mostly attributed them to the fact that I am a heavy sweater who actively cycles, runs, and swims, I figured the head gear and the sweat caused them... Is there anyway to prevent them from happening and cleare them up? Thanks