Post-treatment testing isn’t essential, if you now have symptoms you should present yourself to a doctor asap.
The doctor will advise about the duration of the STI treatment, and how long to abstain from sex for.
For chlamydia for example, the medication is very effective. It usually works within 7 days, however your results could still show up positive for 21 days in total. So follow-up testing isn’t recommended or essential especially that quick.