If you've just started testosterone, it could be your body acclimating to it. Maybe also talk to whoever prescribed it because having the wrong dose could be an issue. Too much testosterone will get converted into estrogen and too little isn't going to be effective. Otherwise, it could just be that you're getting older (monthly stuff gets worse as you age- I used to have no pain and then I started throwing up from it before I went on T and didn't get it anymore).

4 months in and still adjusting dosages definitely still puts you in a range where your hormones are fluctuating a lot, which can definitely cause more irregular and painful periods.