All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
What we understood from your question is that you will pass by the Meeqaat while not having the intention for 'Umrah but with the intention of going to Jeddah. If the matter is so, then you may pass the Meeqaat without assuming the state of Ihraam. Because assuming the state of Ihraam is compulsory only for the one who intends to perform 'Umrah or Hajj as the Prophet said: “These Mawaaqeet (plural of Meeqaat) are for the residents of those places, and for travelers who come through those places with the intention of performing Hajj and ‘Umrah.”
Therefore, if it happens that you decide to perform 'Umrah in Jeddah, then you may initiate your Ihraam from Jeddah as the Prophet said: “And whoever is living within these boundaries can assume Ihraam from the place he starts.” [Al-Bukhari and Muslim]
In this case, you need not to go back to the Meeqaat to assume the state of Ihraam.
Here, we would like to highlight some matters:
Firstly, only thinking to perform 'Umrah before reaching the Meeqaat and then changing one's mind is not considered as intending 'Umrah so that you have to enter in the state of Ihraam from the Meeqaat.
Secondly, menses is not an impediment for entering in the state of Ihraam but a menstruating woman cannot circumambulate around the Ka'bah until she becomes pure. The Prophet said to 'Aa'ishah : “Do all that a pilgrim does but do not circumambulate around the Ka'bah.” [Al-Bukhari and Muslim]
Thirdly, the Muslim jurists have different opinions concerning a person who does not visit Makkah frequently, or does not intend performing 'Umrah or Hajj, whether or not he has to enter Makkaah with Ihraam. The preponderant opinion is that it is not compulsory for him; likewise circumambulating the Ka'bah and performing the prayer in Al-Haraam Mosque is also not compulsory for him.
Allaah Knows best.