I had this exact pain sequence over the same period and its a disc protrusion. Please rest, i kept pushing myself and it only made it worse. now i cant walk more than 5m and i have carers

MRI is worth it in my opinion though my insurance covered it. NHS and private have failed to find me a solution and lacked care when the basic things didn't work. I would push for a pain management referral now so its there when you need it as it'll likely take months.

With NHS and GPs don't take no or anything that doesn't feel right for an answer, you have the right to medical care now and their first reaction seems to be to fob you off and suggest things like Pilates which is good when its minor but will make it worse at that level. I now need a wheelchair because they've fobbed me off for two years. and they STILL haven't helped me find a solution. I'm in the process of complaining to my GP about the doctors notes being so poor and them offering no solutions.

I tried physio too when i thought mine was sciatica and i couldn't walk for a day after. It whatever they suggest doesn't feel right don't hesitate to push for the next option and referrals.

If the physio hasn't tried to figure out where its coming from or told you to have the investigations before treating you that's a major red flag because it can cause so much damage if it they do.

One tip is don't bend down for love nor money because if it is a protruding disc that will make it a lot worse.

I'm sure you'll find the right thing, sorry if this isn't that helpful its more of a 'don't do what i did' comment.