Hi, devon. It is normal for breasts to stop feeling hard and full, and the age you discovered this - at about 10 weeks? - is textbook.
Waking up more is normal - babies do it for all sorts of reasons.
Formula at bedtime doesn't support breastfeeding and the milk supply but many women can 'get away with it' once bf is well-established. I don't understand why you stopped expressing, sorry...expressing would not make you have less milk.
Being agitated on the breast - could be anything at all!!
His weight gain sounds within normal limits to me.
If you are worried about your milk supply, (and as I say, I can't see any reasons for this, to be honest), then you could offer your baby the breast more, and avoid the formula. At this age, there are lots of ways your dh can be involved in the baby's care!
(I am a breastfeeding counsellor with NCT)