Please bear with me as this could be long... 
DS is 6.5 months. Breastfed and has been on 1 small meal of solids for 2 wks.
The first few months were fraught with poor sleeping. Nothing new there then
. After that he became quite predictable with his sleep for a few weeks. He would go to sleep about 9pm and wake once in the night for a feed. I thought "this isn't too bad". Anyway, between 15 & 20 wks he became awful, waking anywhere between every 20 mins and 2 hours all night. Then, aliens replaced him with a baby that suddenly started sleeping through for 10 hours at a time.
Sleeping through went on for about 3 wks. He then went back to waking a couple of times a night. Then back to waking every 20 mins for a few weeks. The last 2 wks he's woken twice a night like clockwork and wants fed before going back to sleep. I know it is habitual though. Anyhow, 2 nights ago we had another awful night and were expecting this to be the start of another few weeks of it. However, last night he woke just once.
I'm so confused. There seems to be no correlation between his sleep and his feeds, solids, what I eat, teething, room temp, etc etc. I'm not sure where to go from here. I have, at times, implemented various sleep training techniques. However, as his sleep is so variable, nothing seems to help. I go to bed at night not knowing whether he'll be screaming in 10 mns for an hour or waking for a feed in 6 hours.
He's also a dreadful daytime napper and I seem to spend most of the day fighting his grizzling and trying to get him to nap. He always wakes after 45 mins. Even if I sit in the room beside him and try and lull him through the cycle.
I feel that we should be tackling his sleep problems but can't seem to pinpoint the problem to tackle 
Any ideas?