Progestogen relaxes smooth muscle and this is what the intestines are. This means that your food goes through more slowly, and as it passes through the colon, where the excess fluid is reabsorbed, it dries out too much, thus slowing down your intestinal transit further.
Fibrous food, like bran, will dry out and make this worse. You need the soluble sort of fibre and plenty fluids.
Eating encourages the contraction of the intestines (peristalsis) which goes down the length of them. To encourage this, eat proper meals, starting with a good breakfast (porridge and prunes is good

) and a nice hot drink (especially coffee - although this may have unwanted effects on the bladder for some of us

) will encourage movement. In theory, this is supposed to help you achieve a good daily bowel habit

(but I must say I struggle). If you look up 'Squatty Potty' it will give you an idea of seating position and the whys and wherefores of that.
Drinking plenty helps - start off your day with a glass of water.
If you know when it is going to happen, you can pre-empt it. Failing that, movicol is good.