I did the exact same work as everyone of the project. We all did data collection. None of us thought up the immunohistochemistry, none of us decided which peptide to explore, none of us came up with the project. We all collected data, simple. If we all collected data, then by the definition yo give, none of us should be on the paper, something I would be perfectly cool about. But, just them and not me, makes me wonder. Even if what they did doesn't warrant authorship - it did, so...
Data collection is definitely worthy of a co-authorship, assuming you did a significant amount of the work. So if your lab had 500 data points, and you collected 100 of them, then ya, you deserve to be on the paper. If you collected 10, I would say you still deserve to be on there, but there are PIs out there who would say you didn't contribute enough. I believe if your work is used in the paper, be it a datum point, a theory, a method developed, or composing the paper, you should be a co-author.
I don't know how your lab works, when I did research, we worked with people from across the country. So we would work up the samples, generate the results, and give them to someone else who would write the paper. The projects tend to be very large, so we looked for one thing in a sample, 5 other labs looked for something else. Anyways, turned out my name was omitted of an abstract because the guy writing the thing didn't know I was working on the project, and my PI didn't know the abstract existed until it was already accepted, at which point the journal would not allow you to add authors. My PI said she was sorry, then emailed them saying anything using the results generated from her lab needs to have my name on it as well. A full article was published, and my name was on it. The omission of your name may not be the PIs fault at all.
Talk to the guy. It will be awkward. These convos always are, but once clear dialog is established, it will be better for both of you. There will be no more beating around the bush, everyone will be on the same page, and there will be less problems in the lab. This obviously bothers you as you made the thread, and have been replying. If you're mad because you were omitted, you'll be mad everythime you go to the lab, you'll cop an attitude somewhere, your work will decrease in quality. You can be candid without being rude. Tell the PI, I worked hard, and I think I earned it. If he says no, ask what you need to do next time to warrent a co-authorship.