In my experience, I've had random reboots for a number of different reasons. It's hard to tell what may be the cause just based on your description. Please provide more details. For example, Does it boot at all and then reboot after some use? Or are you stuck at the boot animation and cannot go to the home screen at all?
And when you said you are on stock ROM, is it the same stock you had before? Or is it a different one?
To share some of the reasons I've had in the past...
1) Incompatible kernel (may not be your problem since you are on stock)
2) Overheating (usually due to overclocking too rigorously and/or wall charging)
3) Messing up with settings somewhere
And as chupi said, just basing on what you wrote, it may be related to one or a combination of the apps you installed. Or, there may be just a bad combination of the apps that you are using.
I hope you have a backup prior to the app installation. That should help narrow down things, or at least go back to the pre-problem stage.
Google Nexus 4
ROM: ParanoidAndroid 3.10 by molesarecoming
Kernel: Harsh Kernel by harsh
Samsung Galaxy S Captivate SGH-I897
ROM+Kernel Official CM10.1 nightlies
LG Optimus 2X LG-SU660 -- Retired FEB 2013