Why am I always having this problem?

Anytime I'm on Facebook or playing a game on my iPhone 4 the app will all of a sudden quit and my screen will go black for a few seconds before showing home screen. My phone is also super slow, can't watch videos or read articles sometimes and the sound doesn't always work. I've tried deleting things from my phone and cleaning the headphone jack and speakers of dirt. The problems persist. What can I do? My phone is old and I cannot afford a newer one or to take it to a repair place since it no longer has a warranty.