As you have missed one of your periods, it would be a good idea to do a pregnancy test. Or make an appointment to see your doctor so that he will arrange for your sample to be sent to the lab for analysis.
As you seem to have irregular periods from time to time, it would be a good idea to discuss this with your doctor. He can order a blood test to find out whether your hormone levels are OK.
Another problem that can cause missed periods can be from polycystic ovaries.
If you are not pregnant, you do need to get investigated to find the cause of your missed menstrual cycles.
Best wishes.
Unfortunately, unprotected sex is never safe. Some women ovulate earlier than others. The pull out method is definitely not 100% accurate as it has a high level of potential human error factored in--not to mention if his pre-ejaculate on a given day happened to have sperm even though he pulled out exactly on time before ejaculating? Take a test just in case it's not just your cycle being irregular.