<human>: Could you distill the essence of the text into 1-3 sentences?

Hey everyone! I'm a newbie here, and I could use a few suggestions. I'm 5'8, 21 years old and I weigh 190lbs. Several years ago I had a trail with a personal trainer who told me my ideal weight should be 130-135lbs. I've finally gotten to a point in my life where I'm ready to work hard at it, so yesterday I started keeping track of my food on my ipod via the Lose It! application which calculates my daily budget without exercise as 1,486.

My real question though is about exercise. I have polyarticular rheumatoid arthritis and at this point I can't do a lot of the same exercises that most people can. I do well on the elliptical machine doing a slow and steady jog, but I can't do it without one because the impact is too jarring on my joints and my knees become too stiff and painful sometimes even for this. Weights can be an issue because my hands flare up often to the point where gripping things firmly can be an issue. Sit ups are only possible on the days my back is doing well.

This is not to say that I can't exercise - simply that I cannot plan certain exercises on certain days because it all depends on which parts of my body are doing better. The point of all of this is I need a little bit of help for exercise ideas - how to modify some exercises or for ideas of low impact exercises I could do. I do have access to a very basic gym in my apartment complex with a few weights, a treadmill, a stationary bike and elliptical machine. 

Also - if anyone else here has a physical disability - how do you know when the pain is normal for you, or if you're pushing yourself too much and will pay for it later? I tend to push myself way too hard and as a result can end up crippled in bed for days. 

I tried a personal trainer once, but he obviously had no idea how to handle a person with rheumatoid arthritis and pushed me so hard in one session that I ended up in bed for two weeks - so I really don't want to go down that route again, not that I even have the money right now.
<bot>: I need some advice for low impact exercises as I have a disability and can harm myself quite a bit with exercising if not careful.