As long as you are not pregnant, there is nothing to do but wait.
Duphaston has many purposes, from helping at-risk pregnancies to not self-terminate, to irregular cycles to treating endometriosis. One of the side effects is that it can cause temporary disruption to the menstrual cycle (even as it treats irregularity!). Wait another month and see if your cycle evens out. If not, talk to your doctor. Do NOT have unprotected sex. Even if you are not seeing your period at the moment, you may ovulate at any time and a pregnancy can occur.