I have an IUD for birth control, but I skip periods sometimes, is that normal? Or can I be pregnant?

Depends. If you have mirena, (levonorgestrel) you may go without a period for a while or altogether. That's expected of it. If you have copper iud, paraguard, you normally would have your monthly periods. If you are in real doubt, $1 pregnancy test from the dollar tree may return your mind to peace.
Yes to both. It is not unusual to have irregular periods with or without an iud. It is unlikely that one is pregnant due to the very low failure rate of iud's. However, it is not 100% and if suspect pregnancy, important to do pregnancy test. If positive, notify md immediately due to the risk of having an ectopic pregnancy.