After the 4.5 update people have been having this issue (including me) and the cummunity has some solutions.
The solution that helped me the most
1. You can change the setting on your router from B/G/N to B/G
The solution that helped some people
2. Reset your routers and your Wifi box (not sure about the terminology but i hope you understand what i mean)
The solution that didnt help me but playstation told me to do
3.Reinstalling from the safemode menu
i would not suggest option 3 because it didnt help me even slightly and it means you also have to redownload every game on your system.
Overall I think yoiu should attempt to exaust all your option before going to option 3 because it takes the most times and has had no reults with people overall.
Option 1 helped me the most but it did not bring it back to the same quality that it was before. My connection since i tried option 1 has kinda been laggy but not as bad as it was and not as consistent.
What's even more frustating is that Sony isn't saying anything at all. WE PAID FOR ONLINE PLAY and they can't even address the issue. How much do we have to pay for you to talk to us Sony?