Change of formula - due to tummy/poo discomfort

Would it be the health visitor we would need to go back to regarding our LG discomfort and possible change of formula. Or would it be the doctors?

I was thinking of just chsnging formula myself and seeing how that goes, but wasnt sure if you actually need to advise someone you are doing it first.

LG is nearly 4 weeks and whatever we have been advised hasnt helped with her poos and discomfort. We havnt slept for the last 3 nights as she is in such a bad way, its horrible to see. Have tried infacol and she seems to fart a lot on it but still in so much discomfort.