holey, not sure that anything in your posts indicate a problem with supply, honestly
There are a few misconceptions in the replies, too, which may be a bit confusing. Your diet and fluid intake will not make any difference to the milk you make, though eating to hunger and drinking to thirst will be good for you. I don't think there is any issue at all with the length of her feeds - it's a myth that short feeds are somehow inadequate and that the baby 'only' gets a drink (this comes from books like the Baby Whisperer, I think). Feeding for a few minutes at a time is on the normal spectrum for babies of all ages (as long as they are the ones deciding to feed for this short time - taking them off after a few mins. is not good of course) and especially so for a baby of this age.
It's the same with expressing. It is normal for expressing to yield less milk as time goes by. Most women expressing longer term will confirm this. It is absolutely not a sign that milk is disappearing.
Breasts do not wear out
Prolactin levels are not really relevant five months postnatal. They are more or less back to pre-preg levels, with only a slight elevation. Milk supply is driven by demand at this stage, not prolactin - you can check the text books for this if you want, or I expect there will be something on line.
Your baby may be waking up for many reasons - teething, need for comfort, emotional needs, growth spurt. I can't see that solids would help, but by this stage, it's no big deal to give a bit of finger food to lick/play with.
Hang on in there - your baby is healthy, you have the milk, and you just need some sleep