raising my grandson

I have custody of my 10 year old Grandson not because my Daughter is sick or because she has passed on because she doesn't want to the courts were going to put him into a state home because she abandoned him and I couldn't see him going there so I stepped in. I have had him since he was five years old, he has been diagnosed with ADHD from one doctor and with Asperger Syndrom from another doctor. His school tells me that he is not a candidate for Aspergers that it is ADHD. Regardless I am at my wits end with him and do not know what else to do. He sneeks food at night then insistantly lies about it even when he is caught. He steals from other household members and lies about that as well once again even when caught red handed! He has told other family members that we beat him and that we only feed him once a day which is not true, child services has come to my house and after investigating it found it to be unfounded. I feel that I'm sacrificing my life for this child and he as well as his mother do not appreciate anything that my husband and/or I do we are both at the point that we don't want him anymore are we being selfish and wrong to feel this way ? We had tried everything from reasoning with him, to taking away privileges,to punishment and yes there have been times when we have popped him on the bottom. All the while his Mother is off doing whatever she wants, whenever she wants and does not help us out financially at all. No I haven't tried for child support although I know that I should. Any advice would be greatly appeciated.