What can be done?

My ex and I have been divorced for two years. During that 2 year period she has moved my 2 preschool children to 2 different schools and 3 different home environments. She also refuses to tell me where my children are living. Each time I find out where she is living, she moves. She has always told me that she and my kids are living with her mother, which is a lie. I recently found out where she is living. (She moved about 5 motnhs ago.)
I have talked with my lawyer and he says that unless I am pursuing custody of my kids, it does not matter where she lives. I would like to pursue custody of my kids, but financailly it is impossible. After paying all my bills and child support, I am left with $500/month which is hardly enough to live. My ex has destoyed my credit so I can't get a loan. I also have reason to believe that she is smoking, drinking, and using drugs around my children (one of my kids has asthma). I feel like I am backed up in a corner. I would like to know what my options are, because I have NO proof, but I know what is going on because my ex's ex friends have said that they stopped hanging out with her because of the drinking, smoking, and drugs. When we were married she never did things like this around me or my children.

Do you have court ordered visitation ?.. cos if you do, then her moving without informing you is enough to drag her butt into court.

As regards to custody.. without money for an attorney, it will be difficult. You might want to see about enforcing visitation first. Has see moved out of state or just within the same state ?

Yes, I do have court ordered visitation. I have just found out where she is living, she has told her everyone including the judge and her own lawyer that she is still iving with her mother. She does not want me to know where she lives I think because of the drugs and other things that she does around my kids. This time I have not let her know that I know where she is living. If I took her back to court what would happen, since I already know where she is living.
She is moving within the city, not out of state. I am trying to get into a position where I can build enough evidence against her to gain custidy of my kids, but I hate that they are having to suffer behind it.

She is allowing me to see the children, she is just not telling me where they live. I feel like I have a right to knw where our children live because I am their father. I also think that she is living with someone else. I am not sure about that either, but if she is, I don't know anything about that person and I should have a right to know that also if he is being exposed to my children.

Hire a PI, get your evidence and file for custody. A PI will be able to do 10 times a better job of getting evidence and it is always better to come from a 3rd party.