Am I doing the right thing??

As  a stay at home mom, we get to experience all the "first's". The first step, the first word, the first eating with a spoon by themselves, etc. Its amazing to witness!!! I feel so blessed to have had the last four years of my childrens life at home with them, so answer me this, why do I (all of a sudden) feel so guilty about going back to work? Is it because I really dont want  to do it? And I am being stubborn and noone is going to tell me I cant do it?? Or is it because I am feeling terrible about the relationship that me and my daughter Haiden are having at this moment? (even if its just a phase she is going thru, and its not my fault) Or is it just because I am scared I will fail with my back pain, and have to quit, and then I will feel guilty for putting my kids in daycare, and for what??? When I couldve just let it go, and stayed at home, and found other ways to occupy my time.
The only thing I do know about myself is that I am not completely happy at this point in my life. I dont believe its my marriage, (my husband is a wonderful man), its definately not my children, they are the highlight of my life, so what is it?? The only thing I could come up with is me not working. The day I got the interview and was given the job, i felt something in my mind and body change....sounds cheesy huh? But its true. Even jon said that I have changed since I have gotten the job, and I havent even started yet. ;) So I guess it is worth a try, its better to try and fail than to never have tried at all.......right?? I think I am tryin to convince myself more than anything. I dont know why. But its damn scary going back into the work force after 4 yrs!!!! I do feel alot better knowing that i am comfortable with this position and this company, it helps!!! lol. So I guess all I can do is all I can do!! until we meet again.....