baby refusing bottle 😩

Hannah
Help! My 3 month baby is refusing a bottle of formula and breastmilk. He would take it just a few weeks ago when someone was watching him but then he didn't have a bottle for maybe 3 weeks and is refusing it now. He is mainly breastfed and I would pump and send it in a bottle and he would take it. 
Should I try switching bottles? How do I get him to accept it again?  I really need him to take a bottle because there are times he has to be babysat.Â