In the movie Hank Pym said that the mass of the body that was shrinkified doesn't change, only the space between the molecules, so Scott Lang always weight 80 kg.
So how was the ants able to carry Scot, i know ants are extremely strong but he still weighs 80 kg.
Later on we see Hank Pym has a freaking Soviet T-34 combat tank on his keychain. Hank must have superhuman strength if he was able to carry a 32 metric tons tank with ease.
Not to mention he shrinked a entire building and was carrying it like a suitcase.