Wetsuit / Extreme swim fatigue

I find that I have to really pull my wetsuit up as high as I can so that there's enough slack in the shoulders. Start from the bottom, make sure you're pulling it up high enough that it fits snug against your groin. You'll have to make sure it's high up enough above your ankle. Then keep going up the suit and pulling upwards. If not, it can feel like it's pulling your shoulders down. Do you feel like you have trouble breathing in it? Too tight around the neck? If I were you I'd explain the situation to a shop and try the next biggest size. 

I've never heard of soaking it before hand, that just sounds like it would be miserable trying to put it on. I always did the technique of putting it on dry and wearing a plastic grocery bag as a sock. That will help slide your leg through much easier.  Good luck!

Yes, getting it pulled up as high as possible is key.  While you can do a pretty decent job yourself, I recently had someone carefully grab the shoulders (from the inside, not digging nails into the rubber) and they yanked hard and up a few times and it made a world of difference!  Good luck to you!

Good advice above.

I'll echo:

#1 - Make sure you have the wetsuit pulled 'up' enough - it should be enough to give you a superwedgie feeling. If you don't do that, the suit can pull down on your shoulders when you extend your arm, resulting in rapid shoulder fatigue.

#2 -  There is a reality that some wetsuits just don't fit on certain people for the seemingly correct size. My first triathlon wetsuit was a BlueSeventy fitted by a very experienced fitter (I put the whole thing on in the store so he could check me out) at a Los Angeles triathlon-specific store, and he guaranteed me it fit perfectly to me, even though I kept saying my arms felt constricted when they were raised (and yes, I did do the superwedgie.) Sure enough, my first 3 OWS and my first 2 OW races were absolute disasters because of early shoulder fatigue in <200 yards, even though you don't use your delts too hard during freestyle swimming!  

My rookie noobness kept blaming myself and my fit for 4 months, and I had like 10 different experienced multiyear veterans of triathlon in the triclub help me pull up that suit. Same shockingly bad result, every time. I even asked here for advice, and then advice was the same - 'you're not pulling it up enough.' 

I finally got so PO'd that I completely ditched the wetsuit at my next OWS and promptly went from far off the last swimmer and barely even surviving 1000 yards, to nearly finishing as the fastest one (of the admittedly SLOW beginner group!) I promptly bought a sleeveless wetsuit and immediately had a totally problem-free Oly swim in my first race with it.  I've since gone a size up with sleeved as well with no problems (I had to cut the legs short.) 

So it's def possible that even an experienced trisuit fitter can get you wrong despite best intentions. Odds are still that you just need to pull your suit up, but if that doesn't work, you may want to size up or try sleeveless.