Lump On the Sternocleidomastoid

hello,

I have noticed an asymmetry in my sternocleidomastoid muscles in my neck ( at least that is what I think they are called); the two big muscles in neck that extend down from ear area. The right muscle seems to have a marble-sized lump on it and the left does not. I was wondering what this could be in the worst case scenario.
I have had swelling problems with my right tonsil for about 8 months now which is swollen.... the swelling goes up and down; same with a gland at the in the neck just under where the tongue is, again on the right side and again, the swelling goes up and down. smoking, caffeine and carbonated drinks seem to make it worse.
I went to see my gp and he gave me antibiotics which seemed to help little so he gave me a stronger course and that helped little as well.
went to an ENT today and he says everything looks fine but failed to explain possible causes for the swellings.
I forgot to mention to him the problem i was having with the right sternocleidomastoid muscle, scaring the heck of of me really. I'm male, 30 yrs old, smoker of 13 years but other wise in good health. And no...no night sweats or loss of weight or even a 'sore' throat, just feels tight. any idea as to what this lump might be and what might be causing the up and down swelling? thank you for any help you can give