I'm at the point in my StrongLifts 5x5 progress where a lot of the lifts are starting to get pretty hard. Right now I squat 205, bench 150, and deadlift 245. So far I've already stalled once on my squats and bench, and on my last deadlift, something just didn't feel right; I barely made by last rep. Also, I'm pretty sure I'll stall on my next overhead press. Barbell rows are still OK.

I'm wondering if I should start doing some assistance work, like pushups or curls, or maybe even some stretching. I know a lot of people will say that I should incorporate some pull-ups, but I'm still a bit overweight (24m, 5'10, 215 lbs) and can't even really do one rep. But if I do start doing assistance work, when should it be done? Post-workout or on off-days?

Any advice would be much appreciated.