My anxiety has been good for 2 weeks, then all of a sudden it's bad again - negative thoughts about my marriage. can this be because i'm due my period?

Possible: It is quite common to experience mood swings and changes with the cycle and just before the period is due is noted to be the time that the mood may drop. This is thought to be due to the dropping estrogen and the elevated progesterone just before the period starts. There are effective treatments, talk to your gynecologist.

Yes: PMS can be associated with anxiety, mood swings, depression, and negative thoughts. It usually starts before your period and gets better once your period starts. It is diagnosed by keeping track of your symptoms thru a few cycles. It is helped by exercise, limiting sugar and caffeine, frequent small meals, and can be treated with SSRI's. Hope this helps