Problem is that I don't feel it when it's happening so I only notice the welts when I get home and they start to itch.
Why on earth would you think it was ant bites? When an ant bites you, it feels like a bee sting. They have formic acid, and you'll find that if you bite them back, they taste just like little lemon drops. You're bigger, you'll win.
As for your bites, they're almost certainly chigger bites. Seem to be a lot of 'em around this year.
GO