use the 7th week protocol and retest your 5RM. Your TM should = 5 STRONG reps, meaning good bar speed, no grinding out a rep, etc...
Finish the cycle you're in and take a deload week to reassess your TM. It's better to error on the side of too light, especially if you've lost a lot of weight.
While a Keto diet is a good way to lose weight, I've ready a couple NIH studies that actually point to a decrease in performance when substituting fat for carbs. If you hate carbs then whatever I guess, I just don't really see the point in a Keto diet. It's a fad diet that works for physique competitors, but isn't really great for performance. If it was, all athletes would be doing it, and not simply handful of genetically gifted freaks.
Your best bet to lose weight would be to establish good eating habits, and ditch the fad diet. Your performance is no doubt suffering from the lack of carbs in your diet, which impacts your ability to recover. You're probably not weaker, you simply aren't recovering.