Ex taking me to court again?

et me try my best to explain everyting! me and my ex wife got a divorce in feb 2010 and i was given 50/50 custody and was order to pay child care 250 health ins 200 and child support of 100 a mth for 1 kid . which comes to 550 amth for 50 50 custody. i have paid on time and have never missed any time with my son . now that i have a new girl friend that she dont like she has filed a motion to modify custody cause i have another kid with this girl.... my son is 10yrs old and is my life. i am not a dead beat dad at all! we fish play sports movies games if you can think of it we do it. she told me 6mths ago she said she was going to national gaurd and now she changed her mind and she is asking for full custody and her rich grandparents hired this bad *** aty and i only have a average aty. its only been a yr since the last order was put in place !!! so what gives her the right to do this to me ??? i need sum help im worried even tho she don't have a leg to stand on it worries me that the fate of me seeing my son lies in the hand of a judge that dont even know me. i bad thing i did do is before he was born i did get in trouble for drug posseion and had to do 120 days in jail. i got 5 years of probation which i walked dwn and completed ..... i read a statisic that states only 3% of people that get put on probation complete it , the rest go back to jail !!! so let me remind u that this happen10yrs ago. so her aty ask me to do a drug test which i did a hair foicle and ped it!!! so i dnt knw wtf is her problem !!! i own my own home and car and have had the same job since 2000. someone say something. o yea i forgot to metion that i helped gave her 570 to help pay her rent . she said she wld make other arrangemets for day care so i wldnt have to pay it if i gave her that money.... then the brat renig and started taking him to daycare without me knowing about on her days . and is saying i refused to pay daycare well i paid it when they called me about and have canaceled checks proving i paid and gave her 570 for rent . she makes deals then backs out wtf