How to help curly hair


So my hair and I have a love hate relationship, and now I’m starting to notice it’s not the same as it used to be. The curls won’t stay and they instead lose there shape and start to frizz almost into a waved curl. Also the top is becoming quit flat and losing it volume, and after all that it’s starting to look dull and un healthy. Does anyone have any tips on what I can use on my natural curls to fix them ????? Or good products for my hair??? Thanks !!!!