My Diva cup is still leaking!!

Sirah

I've been using the diva cup for 6-7 years now. I've had a baby so I had to change to the slightly larger size. I always wear a liner with it because it tends to leak throughout the day. I know I'm putting it in correctly but I don't understand why it's still leaking. Shouldn't I be able to wear it without a backup? Is there a larger cup that I could buy?