The U.N. wonts some of our military to fight for them and we U.S. would not have any control over the UN's army / so if there was a problem between the US and UN we would be fighting each other and that to me doesn't sound right

If that was the case the UN wouldn't deploy US soldiers.
This scenario would be neigh on impossible as it would cause the complete break up of the UN as well as a MASSIVE international conflagration.

Now why would the USA, a country, even think about fighting the UN, an organisation without land just political influence??

If the US is against this UN war, who is to say the US soldiers will do what their UN commanders tell them to do? They would just leave and go back to the US.

And in general because of US funding, and the lack of most other nations to provide UN troops, there really is not a UN if the US was not part of it.