Ask HN: Do you have physical ailments from sitting all day?

I would like to ask you something that has been bothering me for a while.

I develop software for a living and have been doing that for a few years now. I developed leg pain on these past (full time sitting) years. I get this pain specifically where it makes contact with the chair, and then it eventually spreads all over the leg. The pain goes away if I walk around, but almost immediately comes back if I sit again after a short while.

When to have it checked at the MD, but nothing came out of it, he just told me to adjust posture and stretch.

Nowadays, if I am in front of the computer for more than 4 hours per day, the pain starts getting worse and worse. The only solution that seems to work for me is to limit my time in the computer to those 4 hours per day and do other stuff during the day, like exercising for example.

I was afraid this was messing with my circulatory system, so because of that discomfort I quit my job and now I fear cannot/shouldn't comeback to a 8 hour+/day software development gig.. I also have zero experience in freelance, which seems to require almost 8 hours per day as well to be done properly, or am I wrong?

I am fairly young, I’ve invested numerous hours in software development, it fulfils me, it is the best thing I know how to do, not to mention that it is the only thing I have to pay my bills.

I am feeling lost and increasingly depressed by this whole situation. Your peer experiences would be of most value to me. Do any of you have similar experiences? How do you handle it? Did you switch careers because of this?