When Can I Expect A Child Support Payment

My 10 year son has lived with his mom for the passed 7 years,in Aug.2010 he decided to move in with me,because he said he wanted to spend more time with me,and i"m loving it.he is happy to,i don't have to pay 396.00 a month to his mom, but she is not paying me either,my caseworker said it is suppose to start this month,can you tell me when can i expect a payment?