Hi im new to this forum, im hoping someone can ...

Hi im new to this forum, im hoping someone can give me some advise about feeding my 10 week old. Hes been breastfed from the start and has had formula top ups at night since about 6 weeks - now hes really starting to reject the breast and favouring the bottle - how do I get him to still take the boob? reason for formula is i cant keep up with demand - hes also sleeping up to 8 hours a night and im finding my supply diminishing. What do I do?