OK, ds is 5 months and has been exclusively bf, however he is tiny still (5lbs 10 at birth now 14lbs 3oz at 23 weeks) well ok not tiny and putting on weight but still quite littley.
Anyhow, he has been feeding lots and I have been exhausted (also have dd 3) so decided to do some top ups of formula to see if I can attempt to push him through. (I know I know but am feeling v sleep deprived!!!!) So I attempted to a yield to find out how much he is getting. Now either I can't express EVER or he isn't getting that much. First yield yesterday produced 4oz from both boobs after about an hour, tonight not even 2oz
for same time.
I hadn't fed for 4 hours at each yield.
I know he is more efficient than the pump but he is a very quick eater and sucks vv hard but is finished within 10 mins. Urgh, don't know what to think but am I a) producing enough (obviously enough to make him grow!) and b) how can I increase my production?
As an aside my let down is very very slow and I haven't ever "sprayed" across his face let alone the room 
Having been ever so full of myself with other people I am now beginning to feel a bit like I know nothing! Any advice welcome and do you think maybe I just have double cream or am not producing much? I don't want to stop bf but don't mind adding formula where necessary.
thanks