Sudden drop in appetite at 5 months?

My breast milk fed baby (mostly by bottle because he has a low transfer rate and can only get 4-7 oz by breast per day) just went from taking 43 oz a day to about 33 oz a day. Once 6 PM hits, it takes him about 3-4 hours just to finish a bottle, so we are continuously feeding him from 6 PM till 11:30 PM when he finally goes down. He also will only take 1 20-30 minute nap in that 5-6 hour period. He might be teething but we don’t feel anything emerging and he doesn’t show discomfort during the day. He still poops an average of 8 times a day, and we have given him some tastes of egg yolk or salmon mixed with breast milk, but it’s just to taste, not to supplement for milk. It doesn’t compensate for his sudden drop in appetite. Can anyone relate???