Tryndamere hack?

So I've been playing lol for about 3 weeks now, I've learned almost all the champions abilities but Tryndameres seems odd, i was playing master Yi top but i kept dying to tryndamere even though he was level 3 and i was a fed level 5. His Undying rage would restart every 10 seconds but he wasn't even level 6 so he shouldnt be able to even use undying rage. I don't know if its a hack or glitch or whatever but can someone please tell me what this is because this causes me to lose games and it happens a lot ; - ;