Have Cat Questions? Ask a Cat Vet Online.
I am sorry your cat is constipated. You can try adding more moisture to the food so some warm water to loosen the food a little (definitely do this on the occasions you leave dry food down) you can also use chicken stock to achieve this.
There are some other techniques to lubricate the faeces to ease their passage so oily fish (tuna in sunflower oil) or adding vegetable oil to the food can help too (1 teaspoon or so). Liquid paraffin can also be added and this may be able to be sourced from a health food shop or from your vets and this acts as a lubricating laxative. It shouldn't cause an explosive diarrhoea episode. If things aren't improving then you will need to go to your vets as sometimes an enema is needed.
Ok, sounds like a good plan.
You maybe able to get an over the counter remedy at the vets as well that may pack a bit more punch than the oil.
Have a great weekend