How can I tell if someone put an app on my Iphone to spy on me..?

long story short I believe i may possibly have someone reading my text messages. I think my mom put an app or some program on my iphone to read my texts. Because several things lately I have been doing, she finds out without me ever mentioning anything to her. My older cousin put an app on her ex husbands phone to spy on his text to see if he was cheating; she would just sit in the living room reading his whole convo!! Im probably being paranoid but my grandma also said something isnt right, my gf as well.