What is causing the congestion??

My 4m old gets congested EVERY night. Mostly early mornings but last night she woke up at midnight and took two hours to settle because her nose just won’t let her. I’m exhausted because this hs been an ongoing problem since she was 2 weeks. It’s cold and if I turn on the heater it congests faster and yes I have a cold mist humidifier, no it doesn’t help. There’s no visible mucus it sounds deep in her nose. I feel so bad because she wants to sleep, she doesn’t wake right away she tries to reposition herself to where she can breathe and if she can’t that’s when she wakes up really upset and frustrated:(

I’ve been to the pediatrician, we tried reflux medicine as it could be the acid coming up and irritating it. But it did nothing and it made her constipated. Tried steroid nasal spray, made it worse because it seemed like it burned her nose instead.

I’m so desperate at this point, it makes her overtired throughout the day and makes her fussy which I understand. She already only takes 30 min naps throughout the day, she needs good nighttime sleep and the days that it’s not as bad to wake her up she’s a lot happier. I don’t know what to do anymore