Since 3 days, my body/muscles ache, strong headache and feel exhausted! also that my stool color is yellow.and i smoke(tobacco) pretty much.

Viral infection: you most likely have viral syndrom. Please get your liver function , complete blood count and renal functions checked

Rest, pain meds: Such symptoms are usually associated with virus infections. Other serious conditions can cause the same. If pain medicines and rest do not resolve them in 3 or 4 days, or if headache gets severe, or if you start having fever, vomiting, light headedness, or dizziness, then you should be seen by your doctor or emergency room RIGHT AWAY.