i reckon that its perfeclty normal. once babies get a bit older, they will not put on anywhere near as big gains as they do in the first few weeks. and the reason your boobs wont feel as full, is because your body has now settled into a pattern of supply and demand- so it will be making the right amount for exactly what your baby needs, so you wont ever feel 'full' as that is more of a feeling when you are going on 'too' full, if that makes sense? your boobs wont feel as solid, may even go down in size. but its all normal and does not mean you arent making enough.
also the reason for the short burst would most likely be attirbuted to a growth spurt. these happen around 6 weeks and again at around 3 months of age. it can sometimes make your body produce more milk for a while but it will also settle down.
this happens to everyone at different stages (breasts settling and not feeling full anymore)- for some people its within a few weeks but for most its around 3 months and for some not til 6+ months. as long as your baby still has wet nappies and is putting on weight- the number of gain isnt really important, as long as they are gaining and not losing, as like i said previously, their weight gain will be a lot less as they get older- and it even plateau's for a lot of bf babies once they become active and start crawling etc (as in baby might grow in length and head circ, but not gain weight or only gain 20grams, happened to my girls at about 8 months of age- but the growth in height/length, and head circumference showed they were in fact still growing) so i wouldnt worry because you will most probably not get the 300grams+ weight gains per week ever again. that is what babies do in the first few weeks as they build up a supply of fat and their growth is the most in the first couple of months.
so in short. your body and breastfeeding has settled down into the supply/demand and i;d say everything is fine :) baby will probably settle with the short burst of feeding in the next couple of weeks as well