Hi
I suffer from chronic constipation unrelated to my breast cancer (altho it got fat worse after my op and when I was taking pain meds - coxodymol).
The usual and first choice for long term constipation which I use, is peg 3350- brand names Cosmocol and miralax and probably more.
This is gentle and can be taken daily for a long period. The dose can easily be adjusted. Senna is reserved for when things go wrong and backup and a rescue is needed.
Id check with your doctor and if your breast care team if its OK to take this.
Start on a lowish dose, half a sachet I suggest. You might need a lot more if there is back up to be cleared. After it’s cleared drop dose down.
Good luck.
Constipation is no laughing matter!!