I have had a lab mix for 4 years and just got a shih tzu. It has been two days and the lab mix being 4 years old is calm but the shih tzu being 1.5 months is hyper and the lab mix looks at him and wags his tail but doesn't want to be around him. Am I over stressing since its been only two days and what should I do to help them become friends?

Also till now the lab mix hasn't stayed with any other dog. Also both are male.

Let them sort it out, it has only been two days, and yes, both male has a lot to do with it. Try not to get involved in dogdom, just be thankful there is no fur flying, which there won't be. It would have happened by now. They may never be great buddies, it is a pecking order you know!

Yes you are over-stressing. They will bond. Give it time. However, I would never recommend to leave the two together alone or unsupervised. Your big dog could crush that little dog just in play.