How is the mass? Is it a single mass that is coming down? Or is it like a piles mass? Is there any associated bleeding or pain? What is the duration? Are you constipated?
Depending on the answers to these questions it maybe a rectal prolapse which is not very likely considering your age. Or it may be haemorrhoids(piles) which may occur due to constipation.
Haemorrhoids can be treated conservatively initially and if it does not resolve then surgery might be needed.
Neither of the two are unsafe for conceiving a baby.
Next Steps
Detailed symptoms would be helpful in diagnosis
Health Tips
Watch out for bleeding while passing stools