It can be a sudden contraction of rectum but physical examination is needed before making any diagnosis so do physical consultation once .
Next Steps
syrup Movicol BD for 10days (25ml in 100ml water)
it'll improve your constipation condition
Health Tips
please don't do weight lifting exercises for a short period (around 10 days). you can continue it after your health improvement . you can do normal stretching exercise and running/swimming if you want.