If it helps at all.... I found BF-ing during the 1st 6 weeks very, very draining (and I didn't even have any specific problems - no pain or difficulty really, it was just SO constant, and the lack of sleep was such a shock) -
I remember around 2/3 weeks or so promising myself that if i could get to 6 weeks EBF, then I would give one bottle of formula, probably at bedtime, just to make things more bearable for me.
I set myself a deadline of 6 weeks because I knew that then my supply was likely to be well established - if I was going to use formula in any way, I wanted it to be my choice and my decision. I was aware that feeding formula early very often diminishes supply (every one of my friends who fed formula during the 1st 6 weeks stopped BF-ing entirely soon after that - lots of reasons apart from supply there, though). I didn't want to get 'forced' into using it, IYSWIM. Not use formula as a temporary solution and then find that actually, it became permanent.
Anyway, having gritted my teeth and got to 6 weeks, I found that actually, things had improved enough that I put the formula idea on hold... Then a few weeks on from that, I really saw no need.
All I'm saying is that maybe setting a deadline and then seeing how you feel things are going then might be an idea? If then you make a considered and rational decision to add formula, then at least you know that's the case - it won't be a snap decision made under huge pressure after the worst night you've had, for example.
I do sympathise, hugely. I'm very glad DS is EBF, but it really was no picnic to start with. AND I have no other DCs, and can only guess at how much harder that makes the 'prisoner on the sofa' time.