Why my website is taking high memory usage?

Everyone!

I have a website built on WordPress and I'm using Hostinger shared hosting. The website was working fine but now it shows 503 services unavailable error and shows memory usage is high (in H-Panel). Even Disk usage and Inodes are very low under 10% only but memory get high. I've disabled all the plugins and it worked fine then I also changed my theme after that It was working fine but again it started using high memory and when I disable some plugins it comes back to normal. This is not because of a specific plugin/s. Any plugin can cause an error.

Please help me figure out this problem. I've talked to the hostinger they helped me to figure out this but any plugin can cause the issue. So in last, They said we're not developers and they also suggested me to post my query here on"Stackoverflow"

Please help me. Thank you!