First of all , well done for losing the weight that might have been causing the fatty liver.Your doctors gave you good advice and you acted on it, he made you realise that being overweight can affect the insides of your body as well as your appearance. Speak to your doctor over your worries, ask him to be realistic.
It is natural that you worry because it sounds as if you have been watching your mum go through a lot, she only wants you to look after yourself. But please don't be frightenend to live your life. at your age you should not be worrying too much over your lifestyle. You have made changes to your diet, lost weight, get some regular exercise and have a drink at the weekend (unless doctor says otherwise), try not binge but please stop worrying. I have a 20 year old at home, we have a history of alcoholism both sides in the family and i try not to worry about his lifestyle. His urine is very concentrated in the morning (he never flushes the loo), but he goes out drinking most weekends he is the opposite of you never worries over his health, so somewhere in the middle would be good. Don't be too hard on yourself it can make you too anxious and other problems may arise from that.
Mathman, welcome to the forum. It's good that you are taking your health seriously. What we do or don't do when young, and over the years, can affect our later health. If you want to be absolutely sure there is nothing going on with your kidneys or liver, see a nephrologist (kidney specialist) and/or a hepatologist (liver specialist) for more specific testing. I know you said you cannot afford more testing, but you can try the clinics at a teaching hospital. They charge on a sliding scale, according to income, and their services are often free. Otherwise, just continue with your lifestyle changes and be as good to your body as possible. I would advise against drinking on a regular basis, also, if at all.
All the best to you!
You're welcome, mathman. I wish more people would take their health seriously, particularly at such a young age. They could save themselves lots of grief.