Can a judge get money from me if I wasnt working last year receiving Finanical aid??

Last yr I was in jail for 2 weeks and found out I was pregnant. I lost temp custody of my 2 sons from my ex. Criminal case was dismissed. At the time he was being served for support cause I began general tcn in Jan 2007. The Social srvcs wanted money from him. He ended up taking me to court and today Judge said I had to pay child spprt for year when he had custody for $783 a month rating it on the $16 an hour I get now. I have 3 other children and am a single parent. Can the judge really do this?? I now owe $5k and some. When my ex is earning like $39 an hour!!! We have shared custody as of Jan 2008 its shared legal & phscl. I since then, enrolled my sons in daycare through a subsidized program and pay $90 a month. He pays $180 a mnth for the days he has them. Can I fight this??? I never wntd chld spprt from him but Social servcs opened a can of worms for me! Instead he got money from me.. Please help..what can I do..