Sadly I can only too easily believe this is real.
At 11stone and 5'7" you are within a normal body weight and are not overweight.
Caring for tiniest creates wear and tear. I have ended up with excruciating back pain which has taken 7/8 weeks to resolve as a result of: bending slightly to wash my hands and sneezing, taking a plate out of the dishwasher.
Actions now for your back/pain
Firstly, find an expert physio for expert advice and some massage. It is worth £150/£200 for a couple of sessions for immediate relief from massage and advice.
Secondly, the physio will support, I'm sure, naproxen for pain and anti inflammatory impact (with omeprazole for your tummy).
Thirdly, the heat wraps for backs are worth their weight in gold imo.
Longer term:
Sign up for pilates - it is a game changer.
Ask for an appointment with the Senior Partner GP and discuss what happened. I'd also mention your overhang, how the unkindness has made you feel and ask if a tummy tuck might be funded. It probably won't be but put a marker down. I'd also be tempted to ask for a anti-tosser prescription.
Always have some naproxen, omeprazole and heat wraps in so you can get cracking on relief immediately.
I hope you feel better soon. He was an absolute arsehole.