May Allah make your trip and blessed one and accept your prayers and worship, Ameen.
Men have two options when they complete the Hajj or Umra; either they can shave the head (which is called Halq) or they can trim the head (which is called Qasr). The Prophet prayed for those who shave their head and those who trim it, so both are permissible (Sunan Tirmidhi, Book of Hajj, Hadith no. 837).
In your case, it is better to perform Qasr each and every time, and then shave it the last time you perform the Umra. Do not symbolically snip a few hairs from each side as Qasr. This is wrong and forbidden in Shariah. It in fact resembles the Jews who deliberately have uneven amount of hairs on their head. Instead, perform the Qasr at a barber and ensure he does cut an equal amount all over the head.