Radeon RX550

I'm trying to figure out what the happened with my PC because nothing makes sense anymore. I was playing Warframe and it was running normal as usual when I decided to go to the bathroom and when I came back the game suddenly was 20 fps with intense stutters and frame drops even just afk without...

My system is configured with A6 6400k and Asus A68HM K .. so I want install a graphic card on my system and I also thinking to upgrade my system with ryzen 5 1600 and Gigabyte B450M DS3H in future...so which graphic card should I choose Asus rx550 or Gigabyte rx560 OC 4gb..and I am not a gamer...