My son is now 3 years old. He was diagnosed with Pertussis, or whooping cough when he was 6 weeks old. We had a lot of problems with respiratory problems for the next year after that, though things have gotten much better since. He's had normal bouts with colds, pneumonia, ear infections and the like. Currently he is suffering another cold, and this one seems worse than any he's had since the problems with the Pertussis ended. He's UTD on all vaccines. I looked up Pertussis online and it says nothing about reoccurrences of the disease. It does say that older children are at risk after the immunizations wear off, but nothing about a child contracting the disease again. He had a doctors appointment last week, and doctor said it was just a cold, but soon after he started getting worse, coughing to the point of vomiting and he will hardly eat anything. I'm concerned at this point, and would like to get more advice before I ask the doctor to test him for it, as the test requires a long q-tip like thing being stuck way up both nostrils, and is quite traumatizing for a child; he's had this test before, and so has my nephew who is 11, and he said it hurt really bad. I would like to avoid this test if possible.
Please help.

In most cases he wouldn't get it again that soon. More than likely it is just a nasty cold or bronchitis. Has he been running a fever? Does he seem fine other than the coughing? Certainly take him in if you don't feel things are improving or if they seem to be getting worse.

He was running a low grade fever a few days ago. And the coughing bouts today are a bit more manageable. I started him on his breathing treatments, and they seem to be helping, if only a little. Thank you so much DoulaLC, I really appreciate your response.

Glad to hear he is showing improvement. He will likely have the cough for a bit longer, but it should keep getting better and better and become just an annoyance before long. Hopefully he will start eating more and be back to his old three year old self soon.