3 years ago I rescued two cockatiels that I later found out are brother and sister...they have always been together...after they got settled into their new home with me, I thought it would be good to separate them as we'd seen them mating.
They were separated for about 4 months and Sweet Pea was in a cage with Chiquita. One evening, we come home and Sweet Pea was on the bottom of her cage, rocking back and forth and side to side, trembling, panting, and when I went to open the cage door, she hissed at me...I thought...OH NO! She's going to die! She appeared to be very sick.
She let me reach in an pick her up, I'm holding her...which she NEVER allows...trying to comfort her, which she NEVER allows, my husband walks upstairs and I said...Sweet Pea is sick!
I looked underneath her and seen this white "Bubble" and immediately thought the worst...I wasn't even thinking...egg!
My husband says...she's just trying to have an egg....all nonchalant like...I'm all...NOooo wayyy! NO! She's dying!
Well, I put her back and a few min's later...there was a little white egg.

I can be soo dumb sometimes! LOLOL
So I get online, I read, I worry, I feed her calcium rich foods/treats...I always have provided a cuttlebone which she used a lot...every other day, like clock work she'd lay another egg on the bottom of her cage...no nesting material available. She'd go down there and move them around and occasionally "set" on them...kick some out, keep others...I read she'd probably lay a clutch of about 5 or so, and after 30 days I think I read, she'd loose interest and then I could remove the eggs.
Well, she kept laying! I kept removing eggs and leaving a few for her, and she kept laying MORE! In the end, she layed over 50 eggs! I should have taken a picture of them, I was marking dates on the calendar...occasionally she'd lay an egg for a couple days in a row, then go back to every other day or every 3rd day.
I really started to worry of her becoming egg bound especially when the last few eggs had soft spots....I knew this was a recipe for disaster if she didn't stop laying!
To my relief, she finally quit laying! But that was quite an experience!!
This December, she laid 4 eggs, 2 broke and I have 2 I kept for "décor" in an old bird nest we found years ago.
She's never went through a laying stint like the first time...but occasionally she does lay a few eggs...then she's done.
Lucky for me, she's a very very good eater, not much she turns her nose up at...so keeping her healthy seemed pretty easy.
She's 6 years old this year and is housed with her brother again.
As others have said, mating does not mean eggs...she can/will lay without a mating, they just aren't fertile.
Good Luck!
Toni