All perfect praise be to Allah, The Lord of The Worlds, and may His blessings and peace be upon our Prophet Mohammad and upon all his family and companions.
If you want to perform Hajj or Umrah, it is forbidden that you pass the Miqat of your country without assuming Ihram. If you did pass the Miqat without assuming Ihram, then you are required to go back to the Miqat to assume Ihram unless you have already engaged in the rituals of Umrah, then you are free from the liability. However, if you were reluctant about offering Umrah, or wanted to seize the right opportunity to perform it, then you aren`t obliged to assume Ihram from the Miqat; rather, it is permissible that you assume Ihram from your residence in Jaddah or in Makkah if you wanted to perform Hajj, and from Al-Hill (The area outside the Sanctuary) if you wanted to perform Umrah, and you are free from any liability. This is clarified in the Hadith related by Al-Bukhari, and reads as follows: "Allah's Messenger (PBUH) made Dhul-Hulaifa as the Miqat for the people of Medina; Al-Juhfa for the people of Sham; Qarn-al-Manazil for the people of Najd; and Yalamlam for the people of Yemen; and these Mawaqit are for the people at those very places, and besides them for those who come thorough those places with the intention of performing Hajj and `Umra; and whoever is living within these boundaries can assume lhram from the place he starts, and the people of Mecca can assume Ihram from Mecca."
Finally, Umrahs that you have already performed in the above manner are valid, and we pray that Allah Accepts all your acts of devotion, and those of all Muslims. And Allah Knows Best.