Please help!

My little girl is 3 months old now and I am having trouble getting all the gas bubbles out if her tummy after feeding even though I put gas drops in every bottle. Sometimes she will burp and spit up two hours after eating. She drinks formula from the Dr Brown anti-colic bottles and I burp her every ounce and a half because she has acid reflux. I also hold her upright after feeding for 20 minutes to help the reflux. This is affecting her daytime sleep as well because she cannot get comfortable enough to get more than 30-40 minutes of sleep at a time during the day. I burp her mostly on my lap with my hand under her chin, rubbing her back upwards I'm between pats. Sometimes I move her to my shoulder, but she seems to spit up more this. way with the added pressure on her tummy.

Do you have any tips to get the bubbles out of her tummy? I am getting desperate because those 20-30 minutes of sleep mentioned above are in my arms only. When I go to put her down, she immediately wakes up and has a burp a few minutes later.