My daughter just had this in October. Unfortunately in her case she got an ear infection and strep at the same time. Lymph nodes work to remove bacteria from the head...head colds, strep throat, ear infections, etc. (ENT). When doing their job sometimes the nodes do become swollen as they are fighting the bacteria. In some cases, esp with toddlers, the lymph nodes start to get overworked and can't handle the workload that an older child or adult's nodes can handle.
Sometimes, the nodes will win the battle and the infection will go away on its own without antibiotics. Sometimes administering an oral antibiotic at home is needed in order to clear out the infection completely. And unfortunately in our case, my daughter's lymph nodes got so overworked (mind you, this happened within a couple of days and previously her only symptom was slight fever for 1 day) that she ended up in the hospital.
Basically she woke up overnight on a Wed AM...couldn't get her back to sleep. She was running about 100 fever. Treated her with motrin because she seemed uncomfortable, and then at the end of the day she seemed like she was having trouble moving her neck. I called the pediatrician because I was freaked out about meningitis...they told me that as long as she wasn't vomiting and could put her chin to her chest it certainly wasn't that. And that maybe her throat was sore so that's why she wasn't moving her neck well and to keep an eye on it of course. First thing the next morning she still wasn't moving her neck well (side to side or up and down), and her node on the right side was visibly swollen. I took her into the dr right away and they ended up sending us to the Children's ER for a CT scan.
Once a node gets overworked, it becomes infected itself instead of draining the infection out of the body. Then the bacteria starts to spill over into the soft tissue behind the node, and if not caught in time, can form an abscess. What's so dangerous about that is that it will continue to swell as the nodes become more inflamed, and pose a threat to block the airway. So it's treated aggressively. In our case they were able to treat it with 3 days of IV antibiotics...had we waited any longer there was a chance they would have had to go into her neck surgically and drain the bacteria out.
Hope your case is nowhere near as severe as ours was. Sorry for the super-long response, just thought I'd share everything I know about it.