I'm currently using the A&M Forms plugin and was wondering if I can import fields from the native Craft 2 fields? I have already created 20 or so fields that I will use in both the native sections and the A&M Forms sections.
I believe A&M Forms stores its fields separately, it does not use the Craft fields that you would use elsewhere. You'll probably need to re-create those fields through A&M Forms to be able to access them in your forms.
To be honest, you should probably stop using A&M Forms if you are not in too deep. It was never ported to Craft 3 (and never will be), so your site will be stuck on Craft 2 unless you put in significant effort later to switch form plugins.