Lump in throat.

Hi,
I've been concentrating heavily on my dads newly broken after we moved him to a yard closer to home than our yard for 6 weeks. My mams been keeping an eye on my horse for me in the mean time when she goes to check on the rest,
Anyway went to swap them today and to my horror he's quite overweight for one thing but also someone on the yard pointed out he has a lump in his throat. Right in his throat inbetween his cheakbones. Its about the size of a small plum and has a hardish lump inside. Advice was to keep an eye on it for a few days and hope its not strangles??!!!!
Any advice or help on what I should check for. Or what else it could be. He hasnt been mixed with any other horses recently and if it is strangles in real confused because I thought they got ill and lost appetite. He's fine in him self!!
Advice taken gratefuly.

Could be a bug bite, or even allergies. The only way to know for certain is have a vet out to look at it.

Its also been suggested grass glands? Although I've never heard of this theres alot of talk of this online. Anyway apparantly if this is the case it will have gone down by the morning.
If not I think ill take a closer look and probs call the vet.
Thanks for the reply