my website's page was getting cached everyday but since last 2 weeks the website got cached by Google only once. Although the visitors of the website is increased and the content is more frequently updated on the website.
It happens sometimes. I have a ton of websites some of them cached and indexed every day and some of them don't get cached for 2-3 weeks. I have new content on the site every day the issue is not with you i guess sometime that happens.
I think that's kinda normal and at least your lucky enough that Google still cache your website even if it is not that often. I know some site that didn't cached by google for a month. I suggest you continue observing on how often google cache your site, it might help.