There is more danger in this than you think...
The problems are in foods with empty K calories that have all the calories but none of the nutrition. If you don't get the nutrition, you're missing out on all the important vitamins, minerals and amino acids that are needed to keep your body functioning. It doesn't surprise me that you have started becoming light headed, but it can only gets worse and eventually you could end up comatose, being rushed to hospital where I think what you're trying to avoid will be reality.
Drinking tea or coffee doesn't count as a meal, try eating fortified cereals with milk for breakfast, fat isn't automatically bad for you, try eat a protein every day (fish, chicken, beef, soya, etc), stay away from crisps and high sugar foods or anything that says "low fat"
I have lots of good food advice I can give you, but chances are your mum knows best. Talk to someone about it before you end up in a hospital bed.
In the west we say a balanced diet is 5 fruit and veg a day, but that was before we understood nutrition. I prefer what they in Japan, that a balanced diet is eating 30 different things every day.