Hi thanks for asking question.
For stomach pain you can take
omeprazole if pain is because of ulcer.
To treat infective condition like
gastritis antibiotic needed.
You also want to loose weight.
So you just have to modify your diet,take more fruits.
Avoid taking fatty diet.avoid fast food like pizza, burger.
Better to eat boiled diet rather then fried.
Regularly do flooring exercise for 1to 1.5 hour.
Including mininimum 45 minute jogging, running , cycling like exercise.
Effective way to prevent
malaria is preventing its bite.
For that DEET like repellent can be used to spray over cloths or using nets.
Liquid all out also can be used.
Room can be sprayed with insecticide.
Sleeping in AC room is helpful.
Still no benefit then Chen I prophylaxis with chloroquine can be helpful.
I hope I have solved your query.