First of all do a USG of lower abdomen to rule out underlying pathology if any or may initialized with an other pregnancy
test to exclude.
If negative,then don't be much worried as it may be due to weather change,hormonal
etc. Consult with your doctor and take suggestive measures.
Avoid stress by regular deep breathing/yoga,take healthy diet,do regular exercise,need proper sleep and practice safe sex by using OCP or other methods.