What's the difference between cystitis and overactive bladde

Can you please tell me what the main difference between cystitis and overactive bladder is? I have some problems and I did some research, but from what I read about these two conditions I can tell the difference. I have symptoms of both, but I doubt that I could be having them both.

Hello, I am suffering from cystitis. The hallmarks of interstitial cystitis are: daytime frequency (I go more than 9 voids per day!), urgency without incontinence, nighttime frequency and bladder pain relieved by voiding. However, the key difference between overactive bladder and interstitial cystitis is at night. Overactive bladder will have 4 or less voids per night while interstitial cystitis will have many more episodes of nocturia.