According to your symptoms you could be experiencing so called "restless leg syndrome". Restless leg syndrome can be due to several disorders like:
1. taking medicines that cause dopamine blockage - Zoloft (sertaline) is one of them.;
2. pregnancy and old age;
3. iron-deficit anemia;
4. electrolite disturbances;
5. unknown cause (idiopathic)
You can consult some neurologist for some examinations and getting right diagnosis.