soy formula helps stomach. but to ensure your supply doesn't suffer please continue expressing, either manual or using a pump.
also consult another paed to check whether he is fine with breastfeed during diarrhea.depends on how severe it is to be recommended anything other than breastfeed

soy milk formula is usually suggested when child has diarrhea. r u exclusively breastfeeding, how old is your child. you can see another paed to see whether really your child needs something other than breastfeed. also if he goes on soy milk, please express and store your milk, manually or by pump as not expressing may drop your supply

how old is baby?

3 months

should never stop breastmilk even if diarrhoea ..it has immunoglobulins to fight the infection and also it has better nutritive value...

yes its sin to stop breastfeeding even if u r unwell...it is the only milk that has antibodies to fight against infections..infact I should feed him frequently. ..N see some other paed

pedi said to continue soyo with breast milk since he is under weight