In the last few weeks I started writing a lot, which means I also had to sit a lot. Now I have horrible back problems, did you ever have similar problems? How did you solve it?(it’s killing me..)
It doesn’t help that I got a cold and wound infection at the same time..
Tell me your horrible story’s so I can fell better（＾_＾）
Back problems while writing...
You probably are miserable enough, but…
Fix your posture!
Or get a standing desk.
And talk to your doctor, and/or gym coach if you have one, about exercises that would help with strengthening your posture considering your health and condition.
Good luck. 
- Edited
Lappidappi Well, I don't know if you would like to hear this but one of the maternal uncles used to sit on the floor for long periods of time while meditating (religious purposes)
Two years back he had acute pain in his hip area and the area underneath it due to long hours of having his body weight resting on his loins. He had to undergo surgery for that and still hasn't recovered to the optimum health.
I know its not related to writing or my personal physical experience but yeah, he used to sit for hours on the same spot.
My advice: Stand and walk around for a few minutes every hour or so and rub loads of analgesic cream on the area that hurts, cover it with a warm cloth and let the area sweat out. It will help (that's what I do when am in pain)
Congratulations. Keep it up. For health! 
Lappidappi a advice about it.
After an hour or two sitting in the chair, get up and stretch your body, do some exercise, drink water, and then lie down a bit to rest before writing again.
I've been writing for more than six hours in a row, but at intervals of ten minutes to breathe a little. I had no problem with my body.