If a lung nodule changes a little in size does that mean it is malignant?

Yes...and continuing: Very slow growing or maybe stable in size for months or a year only to increase in size afterwards. No one knows the future do you want a definitive diagnosis now or do you want to wait? That is the question.

Not always.: This may mean an infection in the lung or an abscess. It depends on the time it took to change in size. It could be a benign process. But you will not know unless you get more tests, like an aspiration biopsy. It is best to see your doctor and get more tests. Best of luck.