Is this plagiarism?

[ChurchStretton]

I am an amateur astronomer. A few years ago I shared some astronomical discoveries I had made with a professional colleague based in the USA. In 2013 I discovered that most of my discoveries had been published – which was the good news – but that they have been published under the name of the professional astronomer I shared them with 3+ years earlier without a single mention of me appearing anywhere in either the article or the standard catalogue in which discoveries of this type are recorded.

I complained to him - "tough" summarised his 2 line reply.
I complained to the head of the US observatory where he worked - I was ignored, neither of my letters received a reply.
I went through the US based "Whistleblowing" process - the result of the "investigation" was never shared with me.

Am I being unreasonable to think that I have been mucked around long enough and it is time to go public?

church, that's no time at all for a response. Journals take months.

Willie's on the money. Send a chaser - in my own experience, a plagiarism investigation can drag and drag, even when the evidence is as clear as the nose on your face. I've had cases that drag on for months and months when I had 99% matches, because the submitting authors were dragging their feet about responding and I wasn't able to proceed (per the COPE flowchart) without their response. They should be keeping you in the loop however, so no harm in reminding.

Contact someone senior at the Publisher if you get no luck with chasing the EiC. If you get no luck there, you might try RetractionWatch - they're a set of journalists/academics with an interest in the scholarly record, and so might take a look. I'd leave it a solid 6 months, mind.

Hold off on the lawyers - it'll cost you a lot of money and get you nowhere, particularly as you don't have any actual monetary damages to claim.

kerosene i suspect we have similar jobs!