timeless_dreams, It is very hard to find a Karwa taxi. There are plenty of private taxies though.  It is better to avoid them; they might not be very safe. They are illegal anyway.

The ideal solution is to get a car. Doha without a car is a nightmare, especially in summer. Till you get your driving license, you should make arrangements with Karwa (Qatar Taxi Company) to give you pick and drop services on a daily basis. This is the safest option. I used this service a few years ago, it wasn't bad.

United Nations Street is 15-20 minutes drive from Umm Ghuwalina.