Phone locks up for about 20 seconds/lag time. Why?

Hi, I just registered, excuse me for not introducing myself in the proper place, but my phone is pissing me off so much it's the only thing I can focus on.

So...sometimes, when I'm texting, or typing in the web browser, the key will lock up for a little bit before showing up.  I'll just be cruising along, texting, and then I go to type the next letter and it just freezes up for a bit.  Cursor stops blinking and everything.  Eventually, the letter shows up and everything is fine.

That's been going on for quite a while, annoying but not too annoying.  Just recently, however, it's gotten REALLY bad, and affecting more parts of my phone.  For example, I press the power button on the top for a while to unlock my phone, and it remains black.  It won't unlock, just stays black and frozen for a while.  And, when I'm playing with my phone and I get a call, for example, I'll hit the answer button, but it doesn't answer right away, it totally locks up but keeps ringing, and sometimes I'll miss calls because my phone just won't answer even though I hit the answer button about 15 seconds before.

Any ideas?  I'm very frustrated and I like the phone for the most part, but this is getting ridiculous.  It also seems like the battery might be going...charged it all last night, probably 10 p.m.--9 a.m., and by 1 p.m. this afternoon it was already halfway gone and I hadn't even done anything except send maybe two texts.