I think that the bump will go away on it's own if you do the right things. I really can't tell how long it will take to go away. When I have swollen glands they usually go away within a couple of days to a week. But it depends on how congested the lymph is.
Swollen lymph nodes is a sign that the lymphatic system is doing some cleaning, this is a good thing, the body is doing it's job well. What you want to do is help the body along in it's cleaning.
Allergies can also cause the nodes to swell up so I would recommend you have him stop eating all the common allergens. These are wheat, dairy, soy, gluten, eggs, and peanuts. Do not give him ANYTHING that you didn't make yourself. Its probably full of mold and other toxins that only clogs the lymph even more.
If you don't have a water purifier bottled spring water is the best in my opinion, but this contradicts trappers advice and I don't want to confuse you. I personally drink fiji water because I read a study done in Germany where people drinking it improved their health. It is a highly structured living water that comes from one of the few places that is not highly industrialized.
What I have read is that although distilled water is free of pollutants it is not living and has a weak structure, so it takes away your energy to be metabolized, rather than give you energy, just like cooked food and raw live food. But you should do your own research and decide for yourself what you believe is best.
Like trapper says, probiotics would be helpful. I like EarthFlora, which has beneficial soil organisms. This replaces bad bacteria with good bacteria, which helps to clear infections. Google it and you should come up with some articles on the benefits.
everything you said you are doing is good.
You can also give him lots of snuggles while thinking positive thoughts. One woman on the liverflush forum said that doing this changed her child's bowel movements from tannish white, to brown. This should be very helpful.
Feeding him a good diet will make the most difference.
Well, that's about all I can think of. Good Luck!!