How long after taking antibiotics should my swollen glands start to go down?

Usually < 2 weeks: If from a bacterial infection (i.e. Strep throat for neck lymph nodes), groin lymph nodes from leg skin infection, then < 2 weeks. If enlarged for allergies, non bacterial infection, or other than the antibiotics have no impact.

Variable: If the lymph nodes are enlarged due to bacterial infection being treated with appropriate antibiotics the nodes may reduce in size fairly rapidly. If they are due to viral illness being treated inappropriately they may stay large for some time. There is also great variability person to person. Good luck, and hope you are better soon.