Why is my stomach hard after a tubuligation reversal?

Depends : If the tubal reversal was done via mini laparotomy it might take some time to recover but it depends on when was your surgery done, how was it done, what do you exactly mean by " your stomach is hard" is your abdomen tender? Is the area around the scar feels hard? How soon was your surgery etc.. As with any surgery , complications are possible so you should contact your surgeon for follow up.