Sleep training

My daughter slept all night until she was 4 months old. I felt very lucky. To hell with this sleep regression. Ever since then she started waking up initially once then twice n now every two hours. She's 7 months old. My ped says don't feed her just try to put her back to bed. Whatever I put her to bed 9:00,10:00 or 11:00pm. She's awake sharp at 12:00. I try to get her to sleep but then all I could do is keep rocking her. If I stop she's awake. By 3:00am I give up and feed her. Only then she sleeps. Even then she's awake by 6:00am. Some one suggest me something to get her back to all night sleep.