Can amoxicillin control gum infection until I get to the dentist in 3 days? I'm a bit scared of it spreading and the pain is awful. Just started amoxi

It is possible. Antibiotics take about 4-5 days to work and do not appear to significantly reduce toothache. See a dentist ASAP for definitive treatment. Do not delay.
Maybe. It can't hurt, but get to a dentist ASAP.