Can you play Youtube videos by going direct to the site?
When using your phone, have you checked to see if the problem is there via BOTH wi-fi AND your mobile phone signal? (If the problem is only there through wi-fi then it would seem likely that there's a problem with your router. If it's there via your phone signal as well then it must be something else).
My first thought though (without the answers to those questions but noting that it occurs across three different devices) is that your router isn't connecting properly to your ISP's DNS server. Simply removing the power to your router, waiting for about a minute, reapplying the power and giving it a bit of time for all of the lights to come back on as before, might be all that's needed.