How to handle irregular cycle with cyclical progesterone

Since starting HRT in February my periods have become irregular - this could be the therapy, or just because I am 48? I've had one cycle that was only 14 days, and one that was 38 (22-24 days would be my new normal). This makes it really complicated to take the progesterone correctly - I am supposed to start it 10 days after D1 of my period...what if my period starts in the middle of the progesterone cycle? Do I stop taking it and start counting over? What if my period doesn't come when it's supposed to after stopping the progesterone? Both of these have happened. Do I just take it on a strict schedule and don't pay attention to when my cycle comes or doesn't? I'm having a hard time getting straight answers from my doctor's office and wonder if anyone else has had this experience and how you handled the cyclical progesterone?