My lower left leg hurts when I wear certain shoes. Paid a lot for them. Can I have them stretched of something?

Yes. Yes, you can have them stretched but that does not mean that they will become comfortable since you are saying that it is your leg that hurts and not your foot.
Yes you can. You can wear them for a while to see if you can stretch them out that way or else take them to a cobbler who has special tools for stretching shoes out.