Why can't I increase the weight on my barbell row?

That’s it, basically. I can increase, and have been increasing, the weight I lift in nearly every other exercise. I do a full body workout with primarily compound exercises three times a week, and I’m strong—especially for somebody of my size. But for some reason I am almost completely unable to raise the weight on bent-over barbell rows, and to a lesser extent I have the same problem with the lat pulldown machine. I haven’t been able to seriously increase in six weeks, and I’ve tried EVERYTHING: I’ve taken a couple weeks off, I’ve tried drop sets, supersets, rest-pause sets, changing sets and reps, EVERYTHING. Nothing helps.

I don’t know if this is related, but I do occasionally seem to get tendonitis in my forearms that acts up when I do barbell curls. I can up the weight on that exercise fairly easily, and when I get pain I take a week or two off. I could probably use some advice for that too.