Hi and welcome to the site.
Feeling very weak and tired can be normal for the first 12 weeks of
pregnancy. But also it can be a sign of
anemia. If possible a blood count should be checked. Eating foods high in iron may be helpful. Here is a link to a list of such foods to focus on:
http://www.redcrossblood.org/learn-about-blood/health-and-wellness/iron-rich-foods
It's also common not to have much appetite in early pregnancy. This is fine as long as you're taking fluids well. Eat what sounds appetizing. Usually the appetite and the
tiredness go away after the 12th week.
Light brown spots are normal to develop in pregnancy. This is an effect of the hormones. Skin changes are very common. Some of it may go away after pregnancy, but often the skin changes stay.
If feeling very thirsty, it may be helpful to check for
diabetes too.
The stomach overall will feel better if you nibble bland foods like crackers, sip ginger ale and tea and eat what sounds appetizing. SOmetimes
vitamins can contribute to the stomach feeling bad. Crushing the vitamin and putting it into applesauce or yogurt may help.
I hope this information has been helpful.