My toddler (19m) is teething badly waking crying screaming is there anything I can give him? Panadol (acetaminophen) gives him bad constipation as does neurofen

Teething . The symptoms of teething are highly variable between children. He is probably getting new molars. Some children get teeth without any symptoms at all, while others are just miserable. Cold teething rings, pain medications and messaging the gum areas can help somewhat. Ibuprofen usually works much better than acetaminophen. A natural treatment named camilia can help. Good luck!
Cold clothes/ice. I do not like to recommend oracle or things of that nature that's me. I think ice or a cloth wet and placed in the freezer does as good of a job. Usually teethening depending on howb many at one time can last a few days. Just be patient.
Ice & Pediatrician. Intermittent ice can be soothing if the issue is teething. It sounds like a trip to the pediatrician would be advised.