Pain in back

Hi guys, I’ve been training Muay Thai for the last 7 years, but within the last year and a bit, I’ve been getting sharp pain in the highlighted area, when I kick. I have a desk job but I stretch every night and try to activate my glutes and core before I train. I also work my internal rotation, although, my internal rotation on my right leg is terrible.

I’m wondering if anyone has experienced this and what was wrong/how you fixed it. Thanks in advance!