Cluster feeding often coincides with your baby's fussy time. Baby will nurse a few minutes, pull off, fuss/cry, nurse a few minutes, pull off, fuss/cry... on and on... for hours. This can be VERY frustrating, and mom starts wondering if baby is getting enough milk, if something she is eating is bothering baby, if EVERYTHING she is doing is bothering baby... It can really ruin your confidence, particularly if there is someone else around asking the same questions (your mother, your husband, your mother-in-law).
This behavior is NORMAL! It has nothing to do with your breastmilk or your mothering. If baby is happy the rest of the day, and baby doesn't seem to be in pain (as with colic) during the fussy time - just keep trying to soothe your baby and don't beat yourself up about the cause. Let baby nurse as long and as often as he will. Recruit dad (or another helper) to bring you food/drink and fetch things (book/remote/phone/etc.) while you are nursing and holding baby.
Does this mean that baby needs more milk than I can provide?
No. Don't give baby a bottle -- supplementation will only tell your body that you need LESS milk at this time, and that will not help matters. Also, keep in mind that formula fed babies experience fussy periods in the evening, too -- fussy evenings are common for all young babies, no matter how they are fed. The Academy of Breastfeeding Medicine spells this out in their supplementary feeding guidelines:
"There are common clinical situations where evaluation and breastfeeding management may be necessary, but supplementation is NOT INDICATED including... The infant who is fussy at night or constantly feeding for several hours."