K.R.
Fenugreek is an herb often recommended to increase milk supply, but in order for it to work, you must take enough to make your urine/sweat smell like maple syrup. If you took it before, but didn't notice a smell, you were probably not taking enough. Also the milk supply is driven by supply and demand as you probably know. Giving your baby solids may decrease his "demand" for milk and therefore you will begin to make less milk. If you're trying to increase your supply, I would suggest delaying the introduction of solids for a while, and just nurse, nurse, nurse whenever your baby wants. The behavior you described is very common in a 4 month old and is often not related to the milk supply/taste, etc. At 4 months, the baby is much more aware of his surroundings and is easily distractible. The popping off and on is due to the fact that there's just too many other interesting things out there to look at! Try nursing him in a quiet, darkened room for a few days. If the behavior is due to decreased supply or flow, the extra nursing and fenugreek should help as well. If you're still having problems with supply, I agree with other posters to seek help from La Leche League or Lactation consultant.
K. R, IBCLC