8.5 months old.... should i quit bf?

hi mommies, my lo is 8.5 months old and we are still bfeeding. we started solids around 6 months but he is not eating well especially if i try to feed him solids. My problem is that for the past 1.5 months he didnt put any weight... he lost some instead. Do you think i should stop bfeeding and introduce formula milk ( cannot pump). i am really worried and confused. i went back to work at 7 mobths and he is in daycare until 3pm. we bf on demand after and 1 or 2 times during the night and early morning around 6. Is there any mommies with similar experience ?