Problems after ios11.3 update

Hi. I'm having some issues after updating my iphone to the latest ios version (11.3). My wifi connection is absolutely terrible, I can't even watch a minute long video without it buffering endlessly. And the wifi connection drops off randomly no matter how good the signal is. And my phone keeps freezing or randomly shutting down too. Does anyone else have the same issues and if so, what can I do to resolve this? I tried to goodle it and work through force restarting my phone, re-connecting the wifi, switching wifi assist off and on but nothing has helped. I also noticed that everytime I try to turn off wifi networking services, my iphone freezes as soon as i click on location services...it's very bizzare! Thank you.