Is my horse sick?

i have a yearling colt we bought him last year and since last fall he would get stuffed up and his nose wouldnt run or anything but you could hear that he was definetly stuffed up but then it went away then it came ect. now its back i was outside with him today walking him around and he got spooked and breathed through his nose and these big gros bright green goobers were all over his nose so is this something like a common cold...cuz i dont think it is allergies becuase it has just started thawing out and nothing is growing yet.