weaning off breastmilk ??! and behind gross motorly help !

So my son turned 1 on the 29th of December and is EXCLUSIVELY breastfed, literally... he will not eat anymore than a couple bites of any solids and until recently would not take my breastmilk in any form of cup or bottle. Im concerned because he is on the smaller side and is not really thriving physically. He only army crawls, can not pull himself up to stand, barely bears any weight on his legs. Mind you, he has severe eczema and that is said to part of the reason hes not thriving. His doctor would like me to just stop giving him bm and introduce iron rich foods but thts easier said than done. He won’t eat any solids at all now since I stopped breastfeeding, he also won’t take formula at all but he will drink my bm from a sippy cup. Any suggestions? I really want him off my breast period so he can be gaining the weight and getting the nutrients he needs.