Will I always be this confused?

So I've been back to work for a little over a month now and it feels as if I haven't had a break in years and I need one. One day I think that I can do this and the next day I am sure that I can't and am ready to give up and go home again.  I know if I go on disability again it will be for good and I don't think that I am ready for that but I can't shake this inadaquate feeling that I have.  I don't feel like I am up to snuff. I feel much weaker than I ever have been and much less of an asset to my company. I have always felt as if I was stronger than most of the females that I worked with and was very proud of that and that isn't the case any longer. I feel as if I need an excuse for my weakness.  I've just never doubted myself and my abilities like I have lately and I'm not quite sure how to get over it.  I feel this need to go back to my former self and at the same time I think/know (see what I mean) that that isn't going to happen.  I want to get up in the morning before work and run with the dogs, play tennis on my day off and just generally be who I used to be. Sometimes I just feel like giving up. Is it too much to ask to just be normal again?  If I get myself all psyched up to even walk before work it may very well be a day that it takes me an hour in the shower because I'm laying on the tub floor trying not to puke.....then what? I almost wish that I would progress to the point that my choice was obvious. This day to day doubt and undecision is crippling in and of itself.  Of course if I were to progress to that point....oh hell, you get the idea. It's a no win situation from here. I should take the good days and be grateful for them but I am having such a hard time doing that for some reason.  They give me false hope for tomorrow. I just don't know what to do from one day to the next and don't know who to ask.....