MacBook Pro is not maintaining internet connection
I keep losing my internet connections with my MacBook Pro. As a result I would run Network Diagnostics and get inconsistent results. When things are not connected I see red dots by "ISP", "Internet", and "Server". Wi-Fi, Wi-Fi Settings, and Network Settings stay green. I click through each of the questions and at least 9 out of every 10 times, all the colors change to green and I get the message "Your internet connection appears to be working correctly". It WILL then work for a little bit (a few seconds to a few minutes) before then again not working. So I go through the steps again and by the end, the colors are back to green. I never get a message telling me why I keep losing the connection. At first I thought it was our modem, so I kept re-setting it. But nobody else in my family is having connection issues. I have turned off and rebooted my computer multiple times but it has not helped, either. FYI - my wi-fi radar icon at the top of my screen remains dark during all of this, but I will lose access to email, links won't open, pages won't update, etc.
I recently updated to Yosemite but this started before that, although now it is more frequent.
I do not know what else to try. This computer is only about 2 yrs old. Help!!
MacBook Pro (13-inch Mid 2012), OS X Yosemite (10.10.3)