As Bobish suggests, straining is a *bad* idea. It can usually be replaced with patience - a second bathroom trip a few minutes later, or waiting on the toilet for a while. Another thing that might help is a bidet. Some of the symptoms you are experiencing may be related to straining rather than retained stool.
Your body is getting used to a different method of pooping, and your sphincter has a slightly different job than it used to. You’ll get there.