Any time you have unprotected sex (even protected sometimes) you not only take the risk of becoming pregnant, but also catching an STD as well. If you're not wanting to have a baby, you should be using protection at ALL times.
Um...yes. That's how babies are made.
Yes, you can get pregnant from that. Especially if you are ovulating (basically means you are half way between periods). I suggest that if you are not ready for pregnancy that you begin taking some precautions. If you are ready then maybe it is time to start reading up on things you need to know :)
Hope this helps