IPhone 4 help over heat and battery

I have an iPhone 4 and this started happening yesterday, I charge my phone like I do every night, I woke up for school, an I noticed on my way to school, my phones percentage battery would drop literally every minute, and my phone gets very hot. This is the second time this happened. The first time, i let it die out and everything and charged it back up to 100% and by the next morning it was fine. But not this time, I don't feel like it's being over charged cause when my phone reaches 100% I remove it from the charger, but I could be wrong. Any help guys?

It is quite an old phone so could be a battery issue. But based on the fact that it's getting hot it means the CPU is working really hard one something. Try deleting any apps you downloaded since this happened. If that doesn't work, do a factory restore and set it up as a new phone.