As long as you're back and head are flexed or lifted up right by pillows or back support so that you're comfortable lying in bed you should be able to do so. However it is crucial that you ask your plastic surgeon for specific advice. Most patients 3 weeks after tummy tuck are able...
Your incision will improve with time. Incisions continue to remodel for several months and yours will definitely improve. Also consider massage and a silicone based scar cream.
It's unlikely that the "air bubbles" you describe are concerning, but it is truly best to speak to your surgeon. He is most familiar with the details of your surgery and how you've been progressing through recovery. I'm sorry to hear that you don't feel he is giving you adequate time or...