I think Harlow has a cold

He doesn`t have a fever, lack of energy, lack of appetite or anything like that, no weezing, no coughing, no respiratory symptoms. It`s like he has a human Head Cold, he just has a runny nose the last couple of days. But not bad and only really became mucousy this morning when he woke up.
Is there anything I can give him? Like a specific cold tea or a vitamin that would help him fight it off better? ---- Or could this even be a side effect of his last set of shots (including rabies)?
As posted earlier this month, we had just been to the vet for an eye infection (that cleared up right away) and his shots and I dont want to take him to the vet again if I dont have to.