Have you tried a standing desk?  I'm something of a fan.  I currently use a tall chair and a tall desk so I can switch between standing and sitting frequently.  I've seen them work wonders for other people too.  Also, quality chair, important.  Might be related to sciatica?  (not a doc. haha)  But I've seen people battle that in the office setting too.  I've got bone spurs in my neck from too many years of terrible posture at a keyboard.  The only thing that helps me is watching my posture, stretching, and (here it comes) vigorous daily exercise, 10miles on my bicycle.   If I don't do all of those things regularly, I feel my age/damage rather quickly.  So, uh, not really spreading much hope there.. sorry about that.  Hope it's just a bad chair. 

Change the position of your monitor(s), re-arrange your work-space.  That always refreshes my outlook/motivation a bit.

I agree with Septopus, regarding a proper chair and desk.  The money is well spent for your health.

You may want to go for a brisk walk in the morning, or at least prior to when you sit down for a session.

Also, listen to your body.  If 30 minutes is your limit, then get up and move about - stretch a bit, get a drink and all that jazz.  10 minutes break might be enough to continue for another 20 minutes. Although that might be 10 minutes you are not coding, it can be 10 minutes you are mentally reassessing your work so far or planning your next move.

But yes, look after yourself.

Regular breaks are key. OFC the average manager approach here is just to prethend you can sit down 4+4 hours straight at 100% efficiency. As long as you're on you are in control of your own behaviour I strongly encourage taking regular breaks. I used to do some squats and physical exercise too.

And be sure to have some sport outside of your programming hours, preferibly in the morning. You will be considerably less springy, so to speak.

1. Don't use your laptop's keyboard/mouse  (I think this goes without saying, but I am appalled by the number of people in my office using laptops directly. I even bring a mouse/keyboard to hackathons)

2. Get a chair with adjustable armrests (so that you can raise your elbows to your wrist height)

3. Get a desk with a keybaord/mouse drawer, so that your wrists are not strained when you lean back.

4. Get an adjustable leg rest to remove the strain on your legs.

5. Try a "kneeling chair" (https://en.wikipedia.org/wiki/Kneeling_chair)