For the past few weeks I have been getting strange bumps on my wrists, right above my veins. It s happened 4 times now. And it is not an allergic reaction, or not one I can figure out. The first time it happened I was brushing my hair , the next day I was just standing and talking to a friend and it happened again, the third time I was again, just standing and talking to a friend, and this last time I was putting on a shoe. They are a little painful as well as a bit itchy. I havent observed how long they last, because usually I end up going to sleep after it happens. (it lasts at least an hour). The day after, I notice the skin is a bit discolored as though it is bruised, as well as a little tender. The first three times it has occurred on my left wrist above the veins, and this last time it has switched to the right wrist but in the same location. Is there any cause for this?