You can experience very bad or extended PMS symptoms any time, depending on what's going on in your life, and especially if you've skipped a month. You could also just be coming down with the flu, or the stress is just getting to be too much for you, especially if you skipped in December because of stress.
If you are thinking you might be pregnant because of the missed period, it is possible that you may have either had an invalid test or you tested too early. If you skip this month too, you should definitely take another test just to be sure.