iphone6 not working with wifi but wifi is good

my iPhone 6 has not been working properly for last 3/4 weeks. i think since an upgrade . It works fine with wifi off . My iPad and mac work fine with home and other wifi . I have tested home wifi using speed test and it is good.

i have read there is an issue with recent updates causing this problem to iPhone6 is this correct. I can use all my apps , e.g whatsapp, email, bbcweather etc but they are all taking time to load with the wheel going round for a minute sometimes before the connection is made.

I am getting very frustrated as i use my phone a lot. my husband has just bought a new samsung because of issues I am having. I have been into the O2 shop and had it checked by them to see if I had too much data etc but all was ok. I have tried turning it on/off several time but its made no difference. Should i take it to a local apple store?

Please help.