Small for BabyTea it was just after he turned four months, so that's comparable to two months. Not every baby will be the same, of course, but generally things settle down after 8 weeks, and you might start seeing the odd 5-hr stretch.
Just before that point, I also dabbled with the thought of introducing some formula, as all the ff babies I knew were sleeping really well. I didnt though, and lo and behold he suddenly started sleeping a bit longer anyway!
Formula is harder to break down and digest, which is why ff babies go longer between feeds than bf ones generally. But it won't necessarily make them sleep better, and you could find it causes other problems like constipation/wind/discomfort potentially.
You've done so well to get to 7 weeks - I think this bit is the "darkest before the dawn".
Btw things we tried which got me the odd longer bit of sleep to start with:
- I went to bed after the 10pm-ish feed, DS stayed with DH who gave 1am feed as bottle of EBM, so I could sleep until about 4am
- DH slept in the same room as DS and only came to wake me for feeds - it seemed BabyTea would go a bit longer between feeds if he couldn't smell me.
And now he can be right next to me in his crib and sleep for ages!
Hope it's not long before you can get a longer stretch 