Back Pain due to riding

I have a Hunter 350, have done 7k kms on it, 1 year old. Recently I am having a lot of back pain (I am young so kinda sad that I already have back issues), visiting doctor soon. I presume its due the stiff suspension of this bike? I have to ride 25kms(both sides included) for office everyday, lot of potholes and speed brakers on my way.

Please suggest what modification should I be doing to the bike in order to reduce back pain. If you think suspension change won't make the cut, suggest ways one can take to reduce the pain.

Side question: Should I be already looking to buy a new bike which has good suspension like ADVs? This would be a bit hard at the moment as current bike is just 1 year old. Want to keep it as a last option.