Variance in lengths of cycles aren't all that unusual. It is unlikely there is anything physically wrong with you. While some women have cycles that are like clockwork; many others do not and have a great deal of variability in time between cycles and length of cycles themselves. Unless your having unusual changes in the heaviness of your periods, increased pain, something along that line, I wouldn't fret too much about it. Changes in weight, stress, simply changes in hormones as you go from adolescence into adulthood can affect a woman's cycle.

Sounds like you need to continue to work on your anxiety problems with your therapist. Be honest with your therapist about what you are feeling and thinking. They can't really help you if they don't know what is going on.