I've just started with barre chords. I'm not sure if my technique is bad, but my wrist kinda cocks at a pretty good angle. My F chord, trying to barre the first fret I notice my wrist really bends, I can't get it to sound properly or even reach the top of the fretboard if I don't do this. It's not a pain I can tell you that, My arm doesn't lock up or anything, it just gets tired. I'm wondering if I'm playing doing it wrong, or if my wrist just isn't use to it yet, therefore getting tired.
its just not used to it but maybe try to shorten the strap if youre doing this standing up
it eventlually gets better
My gear
Epiphone Les Paul Standard
B-52 LS100 Half Stack
Dunlop SW30 Slash Signature Wah
Digitech Hardwire CR-7 Stereo Chorus
Digitech Hardwire DL-8 Delay/Looper
Boss BD-2 Blues Driver
Fender CD220CE Acoustic
I played on-and-off for a couple of months and eventually got the F chord down without getting tired. Keep practicing it and make sure you aren't bending in a way that will give you carpal tunnel.
Most likely you're just getting tired - probably you're pushing too hard (remember, you only need to exert the minimum amount of pressure - obvious but overlooked often enough!) - but a crappy instrument will make you sweat doing that kind of thing.

If your wrist seems okay for angle just don't push yourself too crazily and you'll be sorted in no time. The F chord's a major milestone for guitarists, enjoy it!
I have no problem grabbing the chord, switching in and out of it. Just getting it to sound properly. Maybe take tomorrow off, as hard as it is, I always end up grabbing the guitar. Hopefully it'll help.
I'd say if you can't get it, the first thing you want to do is play around with your first finger, as in the height of it. Move it up and down until you get those strings sounding clearly, whilst exerting minimum pressure. The other thing i'd recommend is if you're really struggling try it maybe at the 4th fret, where your wrist will naturally be less bent, and move it back towards the F gradually.