feeling so..weak

My poor son has RSV, we are across the map on vacation, and we FLY home tomorrow. He won't stop crying, fussing, being so irritable and today I totally let my guard down. I've been trying to be the "strong mom" and act like I know what I'm doing but honestly...I just can't be strong 24/7.
In the middle of my 4 month old sons breakdown for HOURS and after trying everything in the book to calm him down, all I could do was hold my crying baby with tears streaming down my face as well. I felt lost and hopeless. Being a mother is the best but the hardest thing I've ever done in my life! 
Is it normal for babies to be non stop fussy when they don't feel good? I'm at a loss for words. It's so overwhelming. (He has no fever) just a constant cough and stuffy nose, I'm desperate at this point for any help or tips I can get, please.