I have joint custody of my baby girl and her mom smokes Meth. CPS or the court's won't do anything. Any advice?

I have joint custody of my baby girl and her mom smokes Crystal meth. I caught her smoking it when she was pregnant and I kicked her out. That was 4 year's ago and I can't do anything to get full custody. CPS the Police and the court's won't do anything. They say that I have to have proof but she is conniving and a manipulator. I can't hire a P.I. cause I can't afford it. If I do my own investigating- it's considered harment or stalking. I fear 4 the safety of mt baby girl. I don't know what else to do... Any advice out there.