How to deal with a labmate using my method without credit?
Speak to your advisor. You write that you've already done so but he's like "idk". Well, make sure he knows. Don't "give hints" and speak clearly. If you're assuming that by giving hints he will understand you, don't! This assumption is dangerous, and much more often the other party is not really sure what you mean. Here's an example of giving hints gone bad. The other members of the lab were giving hints to RH88 not to come, but RH88 did not get it, went anyway, and then after he's moved he finds out they were giving hints. 

If your advisor is clearly aware of the situation, knows what your grievance is, and is still "idk solve it yourself", then it might be time to re-evaluate your time in the lab.