[mixmaster]

I have an upstairs office that is always the same temperature as the outdoors. My air cools the rest of the house fine although the upstairs is always a little warmer in the summertime/cooler in the wintertime.
I bought a 10,000 BTU/350 sq. ft. portable air conditioner for the upstairs office. I have it vented to the outdoors. I can leave it on all night and through the day but the room is still 85-95+ degrees. I can feel the frigid air when I stand over the portable air conditioner but the room does not cool at all!
I bought one of those thermometers from an auto parts store where I can shine the laser and it will give me a temperature reading. I plan on zapping all over the room and trying to cover up all the hot spots. I would love to hear from an expert before I possibly waste a lot of my time.
Some technical specs from the office:
It is pretty small, definitely under 350 sq. ft. the portable air conditioner is rated to handle.
One of the walls borders the outdoors, another borders my upstairs balcony. My bedroom has two walls with this same border.
The other two walls border attic space. My house is called 'modern' design. There is no true attic, the shape of the house from the outside is the shape of the room inside. The back wall in this office has a door to the 'attic' which is more like a closet but it is very hot and has a door like any closet would.
The final wall has two small magnetically closed doors that lead to an attic crawlspace. Those two areas are my best guesses for the heat leakage.
If you got through all this text, I thank you for any advice may you have. I see many posts where people try to be brief and end up being confusing so I want to be detailed the first time.