Stress at work, feeling down!

I posted this in my Facebook a few hours ago and thought I'd post it here as well.

I'm very happy about my job, but have been unfortunate enough to first be diagnosed with B12 deficiency a while ago and just a couple of months later I got this unexplainable abdominal pain. Obviously this has meant quite a lot of sick leave from work in the past few months. I was home on full time from late December until mid February and have since then worked 50% again.
Today I went home after just a couple of hours work. The reason I went home is completely unrelated to my sick leave. I was just driving the for me wrong kind of forklift. I get back, shoulder and neck pain from that kind of small forklift so I don't drive it normally, today I didn't have a choice and got all of the above mentioned pain plus that a disc in my upper back decided to lock- something which can be prevented completely if I drive my usual type of forklift.

A while ago I got a slightly annoyed SMS from my boss saying that I should report to him or the supply chain manager next time I go home. Well, I would have done that but seeing none of them were available at the time I just talked to my team leader. My boss also mentioned that my sick leave expired on the 17th of March and he expect me to be back on full time by April 1st. I have been in contact with my GP clinic, but my doctor didn't have phone appointment time until Friday this week, and I was in contact with the clinic last week already.
This whole mess just stresses me up completely. The pressure from my boss to get me back on full time just makes it feel like they want me to resign or something. I know they mean well and just wanting me back on full time, but there's a huge difference of what you want to do and what you can do. I WANT to just send this abdominal pain to hell, throw my painkillers to the moon, but all this misery behind me and get back to work on full time, but the reality looks different. I'm pretty much struggling through my 4 hours of work, get home with a headache from outer space most days along with increased abdominal pain, I simply CAN'T work much more than my current hours now even if I WANT to.

If I just COULD, I'd WANT to work 10 hours per day when needed!

My reality right now consists struggling through my 4 hours of work, constantly being under the influence of painkillers (Ketoprophen ER), and taking sleeping aid pills almost every evening! This is not the life I want to have. I can't even remember what it feels like to not be under the influence of painkillers and no pain, or the feeling of working an 8 hour shift.