Why isnt my cat pregnant?!?!

My cat china is a 1year old lilac british shorthair. I took her to the stud on the 2nd Jan, she mated twice and 2 weeks later she came on heat so i took her again on the 16th Feb an she mated 10-15 times. She was there for 2 days the first time and 3 days the second time. But she came on heat today. Why isnt she pregnant? Even the studs owner was suprised as her male always produces kittens. Could she be infertile?!? 

Thanks!

Some cats show signs of heat when pregnant in the beginning. Also if implantation hasn't happened yet she will not go off heat. I'm not a breeder so I'm not an expert lol but theirs my two cents anyway

There are lots of causes of infertility in cats, obviously all rare since most cats get pregnant very easily.

Since she's had plenty of matings with a proven male there is a problem.  The first thing might be to try her with another male who is unrelated to the first one - it's just possible there is a genetic mis-match between them.  If that doesn't produce kittens I'd be looking at finding a specialist vet - or calling it a day with her and spaying her.

I agree with the above. Both of them even. 

I will add, extra vitamine E (and of course healthy, noursing food)  tipp sometimes the scale in  No pregnancy /no heat cases.

id say she cud be showing signs of heat because she is pregnant and unsure what is happening to her body. wait 15-20 days, get her vet checked and if theres no kittens explain everything to the vet for further checks. IF she dont catch in the next 6 months i would stop trying tbh cus a first pregnancy at 2 years isnt great for your cat x x

The cat's a British Shorhair which is a relatively slow-maturing breed, so the OP has some time to resolve this.  If a different stud doesn't do the trick the problem might be finding a vet they can afford with the necessary specialist knowledge - they are few and far between.

It isn't unknow for a cat to fail to get pregnant by a particular proven stud - this is maybe partly why cats mating freely mate with several males.