is it herpes?

The last couple of months I've occasionally had bumps come up down below which are itchy and turn into red pimples sometimes grow heads sometimes not, they come in clusters and are really sore it's happened 3times in the last 4 months...they stay for about 3weeks before going down...I went down the doctors for a herpes test and all came back negative does anybody have any idea what it could be..on the depo injection also