Will it get better by itself?

Need to examine: It is not feasible to provide a meaningful opinion without taking additional history, physical examination and may be some tests. It would be prudent to see your doctor and discuss if you may be depressed. Counter-intuitive as it may seem, exercise may help. Start with low intensity exercise such as walking and gradually increase the intensity as tolerated. Drink more water. Wish you good health!

Viral: At this time your symptoms suggest a viral gastrointestinal tract infection. Diarrhea will most likely follow. Rest up, drink plenty of room temperature water or flat ginger ale,eat lightly(broth,saltine crackers, toast &no roughage). take acetaminophen for headache &cramps. Kaopectate helps control diarrhea if needed. Symptoms should gradually improve over several days. Call MD as needed.