Samsung J3 wifi problems

Just wondering if anyone else is having trouble with in home wifi?  My phone keeps shutting off the wifi connection if I don't use it for 5 minutes, then I have to sign back on -- my other phones never did that.  Is there some settng I have to change?

When I purchased the phone, I couldn't download apps with the wifi I had.  I contacted the router company and they found another wifi through my ISP modem and that one worked.  They were good and set up a password for that wifi -- but I had to sign up for a $ 300 service agreement.  No choice: ATT, Samsung and my ISP couldn't get the wifi to let me download apps.

About 2 weeks ago, the phone stopped recognizing the wifi password.  I had to contact the router company again and thank goodness I have the service agreement -- she changed the password.  Don't know how long that will be ok.

A bit bothered by this, but I do like the phone, so hope someone has some ideas about thsi...