My 4 year old was covid positive with a bad headache and then was completely fine. now it has been 5 days later and he is complaining of severe neck pain. is this a normal covid symptom in kids?

This is not a "normal" COVID symptom from what I see and hear. But I would ask his Dr, who must be seeing lots of this in Texas and will have a better idea of what to expect in your son based on those the Dr has seen like him in your area. You can also go to CDC.gov and search for symptoms in 4 year olds to be the most uptodate.

Severe neck pain should be further evaluated. Monitor temperature, pain level and breathing. Please see your pediatrician or Pediatric urgent care. Meningitis should be Con, but most likely related to muscular inflammation. Place a warm compress on the area until evaluated. A virtual consultation after the in person visit is available from Healthtap.