Yes it does sound like you have stutter. If you have trouble saying simple sounds such as vowels and constants much less words then I'd say you have a stutter. Fluent speakers can have disfluent speech when stressed but they never have problems saying such simple sounds. You could also have apraxia or dyspraxia. I recommend you visit a speech language pathologist to get diagnosed if you have doubts. I can't see or hear what you're mouth is doing so I can't say for sure. But from what you've described, I'd say it's very possible.