Palpable lymph nodes in neck for months - should I worry?

I have had palpable lymph nodes in my neck for a few month now. I've been sick with the flu, had step throat, my mom died and my grandmother died (stress and grief), and I have three children who have also been constantly sick all winter. I've gotten these nodes checked out via sonogram by three different doctors. No one seems worried. One told me if they aren't gone in three months he'd suggest a PET scan. Now I'm scared. I don't have any wierd symptoms except I'm tired a lot - but I have 3 kids ages 7,5 and 1.5 years old so that's just a fact of life for me. I've also had a chest x-ray (everything is fine), and blood tests revealed that I had mono at one point but it was inactive at the time of the test (which was in December). The blood tests also showed that I was slightly anemic, but I am a vegetarian, and that could very well be the cause of that. No night sweats or fever, nothing strange. Except that I am extremely anxious about this!!! Are palpable lymph nodes that have been there for a while always something to be worried about?