I have a red bulb, almost like a blister, on the tip of my penis. Is it herpes?

I have a red bulb, almost like a blister, on the tip of my penis (right on top of the hole.) It doesn t burn when I urinate and I m able to ejaculate just fine (though, to be honest, I ve refrained from doing it because I m afraid) I haven t experienced any itching or burning sensations. I haven t found any blisters or warts of any kind and there isn t a rash. I also haven t had any discharges. Please help! I don t know what this thing is and I m terrified of what it might be! I m 19 and sexually active. I don t think it s herpes but I m not sure. Thank you!