Tried anal masturbation using vaseline as a lubricant , then read on internet that its harmful? now im anxious as my stool is slightly different. will this go away and everything return normal again after a few days?

Vaseline doesn't harm the anus or rectum in any way; there isn't any reason to avoid such exposures. Your "different" stool isn't because of that event. Everything should be fine very soon.

Use a water based lubricant and if no change in stool than continue using. Both are not harmful. If any more problems arise in stool than see a proctologist or a gastroenterologist.