ling, me tbf, my boy is now abt 8wks old, let me share w u my experience for past wks. since ur bb is abt 3wks, perhaps his having growth spurt. when my boy is having growth spurt, he'll cry for milk every hr. during growth spurt, bb aso tends to get fussier, so maybe u thought he's still hungry tho he has latched on for 45mins. in fact, during this period, instead of giving FM, it's better tt u latch him on more frequently as it helps to increase ur milk ss. u can read more fr
http://www.kellymom.com/bf/normal/growth-spurt.html &
http://www.mother-2-mother.com/cc-baby-B.htm#Fussiness.
aso, wat u pump out doesn't mean tt u hv low milk ss, aso it's common tt e output is low esp aft u just finish latching ur son directly, read this
http://www.kellymom.com/bf/supply/low-supply.html. if u still can pump out something aft bb finishes latching means u actually hv quite a gd ss. during my 1st few wks, i aso can oni pump out abt 20ml for both breasts aft pumping for 15mins ea side. don't be disheartened, keep on nursing & pumping, increase e pumping frequency & over e time, u c tt e output will increase. like me, fr 20ml to 40ml, then 60ml, then 80ml, now switch to electric dual pump, can pump at least 80ml, many times got 100ml & sometimes 130-160ml. watever pump out is actually excess as bb has aredi already been fed thru latching.
impt thing is tt u hv to monitor ur son no. of wet/dirty diapers & if he's gaining wt, don't top up with FM & don't need to be too worried abt wat u pump out. note tt supplementing w FM will actually decrease ur milk ss. too over concerned abt wat u pump out will make things worse cos e output will be low. initially, i always look at the bottle to c how much milk i pump, output v.low, now i don't even look, surf net when i pump & i get more output. some form of distraction actually helps to increase ur pump output.
i'm not expert myself but just hv to read a lot to find out more & cope w e different situations, so just sharing w u wat i've experienced.