Talk to General Practitioner on Left Side Lower Back Pain

Hi respectables, back in 2018 i got back injury during squats exercise but its was get better after a few weeks till then to now I do not masturbate regularly, but when I do, it pains in my lower back left side in last joint close to hips and stays for a week or so and then goes away. If i masturbate again within this period, it will increase even more. My pain makes it difficult for me to some lye down as it constantly keeps paining and even when i sit down form meal on floor its start hurting. I suspect this to be related to my prostrate gland but not sure. I gain my weight i that period about 12 to 15 kgs. I can't do gym muscle exercise, pain starts again. Please help.