"With all of the latest hullabaloo about cell phones being used as bugging devices, you may be feeling a bit creeped out at the prospect of being monitored without your knowing it. Although some cell phones can be remotely programmed, most modern cell phones would require physical access to your phone to tamper with it. Luckily, when cell phones are transmitting, certain tell-tale signs can be a dead giveaway that your phone is being monitored."
This is an answer posted recently to a similar question. Hopefully it can be of help to you.
"You can check your last account activity to see what devices have logged into your account, when and from where. This should give you a pretty good idea whether anyone has access to your Google account. It is a straightforward process:
“To see activity for your entire Google Account, go to security.google.com and click Recent activity under “Security” on the left. This page includes security-related actions you’ve taken, like signing in to your Google Account, changing your password, or adding a recovery email address or phone number.” https://support.google.com/mail/answer/45938?hl=en
If you think that someone has installed some kind of monitoring software on your phone, the simplest and most effective thing to do is a factory reset. This will erase everything and return the device to the way it was when it left the factory. Make sure to backup everything before you do this, or it will be gone forever. If you decide to do a factory reset, it should be in your settings under “Backup & reset,” although this varies somewhat from device to device."