If I had sex about 1 month ago and used no protection and was on my period would signs of a serious diseases that could be dangerous, would it show up in that time?

I have two questions that I'd love to get answered. From the answers I've read here you give really good answers to most the questions.

I'm on hormonal birth control, and I was late with two pills this past week and had missed one a bit over a week ago. Yesterday me and my boyfriend had intercourse twice and he came in me both times. On the info-thingy that comes with my pills it says that a missed pill in the third week of active pills don't compromise my protection as long as all the others are taken correctly. But I'd been late with two.. I tend to get extremely worried for no good reasons (I was worried I might be pregnant before I'd even kissed a guy and before I got my first period...) so if there was no pregnancy risk I just need to have heard (uhm, read?) it from someone whom I consider an expert.

I also wonder how much of a risk for an STI a guy going down on me would present. I know I'm clean now, but when I was still single I was at the receiving end of unprotected oral sex and I really want to know how much of a risk that is for me and how big of a risk it was for the guys in question. Thanks for taking your time with this question.

I have many small red dots / spots on the tip of the penis. It pains during masturbating and during bathing in warm water. These red spots have come only recently, probably, some days after unsafe sex with a guy!
What could this be!
Is there any medicine that I can take.

I'm 16 and I've been thinking about having sex with my girlfriend for awhile now: she is ready, I'm still deciding but I think I will with her eventually when I'm ready. When we do there is no doubt in my mind that I will use a condom and I already have one but I really dont know much about them because everything I hear from programs at school or whatever is don't have sex, sex is bad, you're not ready, etc. I never hear anything about having sex but with a condom really I know there is a chance of the condom breaking but exactly how big of a chance are we talking about here because a 10% chance and a 90% chance are two totally different things. Also is there a way for her to get pregnant if the condom doesn't break? I don't know how that would be possible but that's why I'm asking because I don't know, also can stds be transmitted while using a condom even if it doesn't break?