You're not necessarily having trouble recovering.
After a year is usually where new lifters start to plateau from a linear progression of just adding weight. i.e. The End of Noobie Gains (as they say)
Sometimes just switching the style of programming will jumpstart your progress.
First off - Make sure your nutrition and sleep is on target (those are the ...
There is an entire science to your question, called "anti" workouts. The main goal of the core is to resist tension, not flex or bend, which is why your back might hurt. If done correctly, this shouldnt put ANY pressure on your back(if it is you arent doing it right).
Resisting extension, vertical pallov press, ab wheel rollout, ...