can you check these

you cannot eat a lot of chocolate
tu ne porrais pas manger beaucoup de chocolate

you could go running every weekend
tu porrais aller courir chaque week-end

you couldn't go swimming after you just ate
tu ne porrais pas aller nager apres que tu as mangé juste

thanks in advance :)

Some spelling = cannot could be Present Indicative = tu ne peux pas or Conditional te ne pourrais pas

Were you told what tense to use?

With can not, I'd use Present Indicative but with could = Conditional

If you use après que you will need the Subjunctive. This structure is far easier: après avoir mangé OR because of the word "just" après être venu(e) de mangé.

Sra (aka Mme)