Honestly Tryndamere is strong in low and even high elo. In my opinion his only true counter is 


are good vs him in early, but whenever trynd get to mid game, or jungler helps him u are doomed, they can't really outduel trynd later, they can just def tower from him if they don't stomp him early, so if u are playing these champs ask jungler for help to shut down tryndramere more in early game.
is a champion who can duel vs him except nasus in mid-late game, but you don't really counter trynd with jax, it's more a skill match up, as jax u can't do anything vs him early, he outdmg u and outsustain u. After trinity dueling is 50/50 and maybe after sterak/ shojin your chance of winning duel vs him are increasing, just be sure whenever u get him to low hp and he press r stay away from him unless u got your e.
also skill match ups for trynd they can just poke trynd, hit and go back, nullyfying his engage, trynd later can 1v1 them but still, he must be careful.
I didn't see any of this match ups, most of them trynd will have problems early, but vs urgot R he can press his R, vs aatrox he has enough mobility to escape his combo, kled and camile has insane early, but if jax can solo both of them later then trynd can do it for sure.