No tummy time help

A🌸

I can not do tummy time with my 10w old baby. She is always eating and I have to wait 2-3 hours after to even try or she will spit up and choke on it. I’ve tried doing smaller more frequent feedings but she just SCREAMS for more and the pediatrician said she is a little underweight for her height (she is a tall lean baby)

I’ve tried the boppy pillow too for tummy time but she still spits up. She is only formula fed and is on enfimil AR which is for spit up, she has acid reflex.

I feel like she is behind now :(. She does however hold her head pretty well I think. When I put her on my lap and hold her chest she can sit there for awhile controlling her head movement. Should I just keep practicing with her like that? Or if there another trick I can try for tummy time.