Student or Learner
I would like to know if there is any difference between since and ever since. For example, Can I use both in the following sentence? I have been happy since ( ever since ) I won the lottery. Can I use them interchangeably? Thanks for your help.
In the context you gave, they mean the same and are interchangeable. That is not always the case.
I have had three baths since 2012. (You cannot use "ever since" here.)
I had a shower installed in 2012. I have used the shower instead of the bath ever since. (You could change that to "since then" but not to just "since".)
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.