Hi there he sounds similar to me I had tonsillitis in April gave me antibiotics for 5 days and it came back 5 days later but worse couldn’t open my mouth went urgent care they put me on 10 days blood came back normal and throat swab came back negative. A week later it returned again Gp gave me 5 days different antibiotics 10 days after last dose it bloody came back but this time not so much pus on tonsil but ulcer on left tonsil she did throat test and urgent referal ENT and she gave me same antibiotics I had last time 5 days worth. So ENT 5 days after and he basically precined me Co-amoxiclav for 10 days and perdislone steroids 5 days and so far it hasn’t come back it’s been 2weeks touch wood! In the mean time my throat swab came back as strep. Maybe your son needs another throat swab as mine initially came back clear. So I suffered reoccurring tonsillitis for 3months but only the last month was diagnosed as strep! Ask for different antibiotics as the usual ones they give would take the problem away but it would always return. 

My husband had the same issue but his nurse practitioner put him in a 2 week wait.

He saw ENT they said he was fine. This was in January. He still has 1 swollen tonsil (which they've asked if he wants his tonsils out) but he's feeling better in self now.

Hopefully similar thing for your son x

He doesn't actually have any signs of infection and he isn't in pain. With a clear swab and no pus or spots they won't prescribe him any more antibiotics which I understand. His current symptoms are just the one swollen tonsil and glands and feeling unwell/weight loss. I was hoping we'd get to see ENT soon and they'd put my mind at ease but it's not looking like his appointment will be anytime soon and I just feel bad that I can't do anything for him and I'm worried incase it's anything serious. 

Thank you that's reassuring that your husband is feeling better now even with the swelling.