This is a topic where the schools of jurisprudence have different positions. The Shafi'i and Hanbali schools permit performing multiple العمرةs in one trip, citing the hadith where النبي (صلى الله عليه وسلم) instructed Aisha's brother Abdur-Rahman to take her to Taneem to enter الإحرام for a second العمرة during the Farewell الحج. The Hanafi school generally permits it as well.
The Maliki school and scholars like Ibn Taymiyyah consider performing multiple العمرةs in one trip to be مكروه (makruh). Their reasoning is that the companions of النبي, despite living in or frequently visiting مكة, did not repeatedly perform العمرة. They advise that voluntary الطواف around the الكعبة is more meritorious for someone already in مكة than going out to Taneem to re-enter for another العمرة.
If you choose to perform a second العمرة, the process is: exit the Haram boundaries to the nearest Miqat point for مكة residents, which is Masjid Aisha (also called Masjid Taneem), approximately 7 km from the Haram. Enter الإحرام there with the intention for العمرة, then return to the Haram and perform the complete العمرة rites (الطواف, السعي, and hair cutting/shaving). There is no fixed waiting period between العمرةs. Many الحجاج perform a second العمرة on behalf of a deceased relative or someone unable to perform it themselves.