Refusing to feed during the day

Hi, my baby is now 3 months old and for the last few days has started refusing to feed during the day.
She has also started waking every 2 hours at night. I am exhausted how can I switch her round?
I thought she may have been teething but not so sure now, she doesn't seem poorly and has enough wet nappies and poos.

I had been feeding every 3 hours or on demand and it had been working fine although she isn't what you'd call a hungry baby. Yesterday she hardly fed at all so I am starting to worry about supply. Has anyone else had this?