Stretching doesn’t mean you have to crack your back a gently stretch is more than enough not forcing your body when it’s not necessary. One of the most important things when you are stretching is breathing in when you do the stretch and out when you end it.
I would suggest doing planks daily could help strengthen those back muscles as well other benefits such as core. Slowly increase the time of the planks each day, starting at a minimal time so there is low opportunity for damage.
It means that you didn’t stretch properly. Sometimes, it happens to me too – I’d suggest to ask a professional or a certified yoga teacher (someone you can trust) in order to understand how your body works.
Depends on how weak your core is. If it’s as week as mine was then start with three days a week beginners yoga. Start working on your plank, squats and full body flexibility and mobility stretching
Make sure u are doing the correct stretches and not puttin too much strain on your back. Yoga is good for all body parts, you can try that. Stretching should feel good and loosen you up, not restrict you, leaving you in pain