My cat is heavier than she has ever been?

Well, my cat has had a bit of a runny nose or something like that because when she purrs it sounds nasally. I had asked on yahoo if anyone knew why but I only got 2 answers and they weren't very helpful -.-. Anyway, I picked up my cat, and she felt heavier than she has ever been. She is not fat, and she only eats 3 times a day: morning, midday and night time. Could her dry food be making her heavy? I'm not sure if she has been desexed, so could it be kittens? I hope she's okay... I seriously need some asnwers, I feel worried about her. Thanks. x