Naturelover,
My ds is another milk vampire, except he is nine months old. Feeding (and sometimes biting) during the night but very distractable during the day.
I do the same as you & feed lying down in darkened rooms etc. etc. but it doesn't make that much of a difference. He does feed a little longer when I pounce on him boobs akimbo the moment he wakes from a snooze; this might help you too?
A few suggestions.
Re: the being worn out. What time does dd go to bed? One thing that helped me was to put ds to bed between half six and half seven, which gives me much-needed "me time" before he wakes. I can use this to sit in a comfy chair & watch TV with dh, or have a warm bath, or if I am really knackered, go to bed early.
A bedtime routine helped him go a little longer before his first night waking; ITNG, massage, feed then book (so not fed to sleep) then cuddle to sleep. First and second time he cried a lot but only whilst I was holding him, so I didn't feel too bad; third time he went to sleep almost immediately and most nights still does. It means I get four even five hours in the evening.
Co-sleeping helps me with the night feeds too but I know this isn't for everyone.
Also I keep the lights dark at night so he learns to associate night with sleep; he now goes about four hours between night time feeds (although sometimes they roll into one and I wake up at seven barely remembering how often he's fed) whereas he was feeding two hourly.
I hate to say it, but weaning ds made no appreciable difference to his night time sleep. But the time in the evenings, and the co-sleeping made me much less worn out.
As for the teething, ds luckily never showed much signs of teething discomfort so I've no suggestions here!