Sick baby, need opinions 🙁

My son is almost 4 months now and he's been sick for the past 2-3 weeks. It seems just like a cold but it's getting worse not better! I've taken him to the doctor a few times and they just say the same things just let it pass on it's own and they sent him for an X-ray to make sure it wasn't pneumonia (it's not). I just don't know what to do I feel so bad for my babe and it's really scary sometimes. He keeps getting low grade fevers of 100-100.4 and he's congested in his face but no runny nose, he has a cough which seems like he's choking on his own mucous. I just want to make him feel better. He's eating okay and making wet diapers plenty, but he's kind of fussy with the occasional inconsolable screaming fit and he's down he just wants to be snuggled. Any other moms had a baby this young be sick like this? The doctors say just let it pass but obviously I'm going to worry that it's only getting worse. Idk what to do!