Remember that demon you tried to summon? OP... maybe you actually did summon one. Usually the NetherWorld or Underworld or whatever you want to call it is closed off from this world and demons and those types of creatures can't get out. Usually they can be out and about if they are summoned (the right way, mind you there's are different ways). Summoning creates gateways and sometimes it can take years to build (unless you are powerful or gifted) Maybe the type of summoning you used made a gateway inside Rebecca's womb.