What Causes Itchiness And Small Blisters On Penis?

there is an area on the shaft of my penis just under the glans that became itchy and has now broken out into a small open sore smaller than the size of a pencil eraser and another area that has three very small open sores that appear to be blisters. I first notice this 3-4 days ago. Could this be from too much sex, poor hygiene or possibly a sti?