[Amanda808]

I use the swipe lockscreen which works fine when selected, but after a few days it randomly turns off and goes to no lockscreen.

I also discovered tonight that my phone turned off my do not disturb mode. I've tried googling, but no one else seems to have this problem.

[B. Diddy]

Welcome to Android Central! Do you have any of the Smart Lock functions turned on, like Trusted Faces or On Body Detection?

[Amanda808]

No. I've turned them all on at some point while learning how to use my new phone but ultimately (I believe) I turned everything else off.

[B. Diddy]

Go to Settings>Security>Smart Lock​, and make sure all of them are turned off.

[Amanda808]

Smart lock is greyed out and I can't select. I'd assume that means nothing is selected?

[B. Diddy]

Probably. Go to Settings>Security>Trust Agents, and see if Smart Lock is turned on or off there. Try turning that on, then go back to the Smart Lock menu and make sure all of that is turned off.

Try also wiping the cache partition, which won't erase any personal data: http://support.t-mobile.com/docs/DOC-10404