Keeps getting sick

A

Ok so I wasn't initially worried about my almost 6 m/o getting a cold when it first happened. He's my 2nd baby so I know they have to go through these things but OMG I'm at a loss - this is his 4th back to back cold! I just don't even know what to do anymore. Nose Frieda, humidifier, elevated mattress, mommy's bliss for cough, warm fleece clothes,.... what else can I do to help? It's been almost a month. Just when I think he's getting better he ends up with a new one and this time he had a fever too. I know most of its germs. coming from my oldest's preschool but I wonder if it might almost be a combination of teething or something else. I don't even know what to think anymore. Any other suggestions would be so appreciated.