Why can i not go for a bm when on my period? after my period i feel quite poorly then it settles down after 2-3 days before the cycle starts again?

Leading up to/during a period, the gastrointestinal system is affected by hormones, both in propulsion and in absorption. The body is also likely a little dehydrated (more water being absorbed and retained). This can lead to lack of BM for several days. Make sure you are rehydrating with copious water and electrolyte solutions, eating fresh fruits and veggies for fiber, and continuing exercise