Upper respiratory in kittens

My kitten is 7 mo old now. He was 4 mo old when I rescued him from a shelter. Heis sneezing alot of snot up,I try to wipe it but he runs and sniffs it right back up!! He's been to Vet several times but is not any better.After reading this rorum I started him on Lactoferrin. It's been a week, but no change yet. He's been on lysine since I got him 2 mo ago. Praying he gets better real soon. How long will it take to see an improvement??

Maybe see a new vet?

Is kitten on antibiotics (for secondary infections)?  Are kitten's eyes goopy with mucous as well?  If so, did the vet give you antibiotic eye ointment?  Did he suggest a room humidifier on a temp basis for any congestion (use only if vet determines necessary)?  Is your kitten eating well, or is he lethargic, dehydrated, anorexic?  If so, new vet immediately for possible fluid therapy, evaluation of the nasal passages, mouth/throat exam for ulcers (calicivirus potential) - any of these observations found could indicate the need for additional medication to help him recover.

If it's been longer than two weeks since the first sneeze/sniffle, please consider seeing a new vet with a new evaluation ASAP.  Early and effective treatment in young kittens can help prevent herpesvirus from becoming a chronic condition (assuming this is a URI, otherwise it would be wise to rule out something else like allergy, dust or house mites, foreign body in the nasal cavity etc - you want to have all your bases covered).