Introducing estrogen into your system will generally reduce your testosterone and, therefore, also generally reduce the fullness of your erections. I hope that was explained to you when you were prescribed it. As for the testicular pain, if it persists for too long see your doctor...it could be a vericocele, an infection or something got twisted, but it is not likely to be caused by the estrogen.
Estrogen treatment will reduce sperm count but I wouldn't rely on it to make you fully sterile.