Service Unavailable - Error 503 on hosting a .NET website on as shared server

I have hosted my website on a shared server (BigRock, BlueHost). The site used to run fine but for the last couple of days I have been getting: Service Unavailable error - Error 503 every few minutes.
The issue creep-ed up from no where as there weren't any changes/updates made to the site and it used to work just fine.

On checking with hosting providers, they mentioned that due to extra resource utilization the IIS pool is refreshed. The suggested optimizing it but I am at lack of any solutions.

Any help is much appreciated.