Welcome to HCM
First of all, where was this cyst
you are talking about.
There are many cysts which can occur, most common being cysts filled with sebum and present on hairy skin. These cysts recur if not properly removed. each cyst has a capsule and complete removal is ensured when you have removed with the capsule.
There is another scenario which could have occurred. The suture line could have got infected. This is due to inadequate dressing of wound and improper therapy of antibiotics.
You should get back to your doctor who did the surgery and he would help you deal with it.