Greetings, sorry about your concern.
Your description is very much a muscle pull rather than a nerve. Always remember nerve will not be troubled at any point unless a deep cut injury.
Next Steps
if you are an individual who can self manage your problem start hamstring stretching four to five times a day. you will improve and pulling will be lessened. Alternatively you can see a physio who is well versed in musculoskeletal issue and exercise protocol. normally physio will do trigger point release (meaning releasing tight muscles) , stretching and strengthening of core muscles.
Health Tips
doing the above said will get you out of your trouble. Remember never be fooled by disc problem or similar advices. nerve and disc will only be a troubled in cases where there is a severe trauma. if any concerns do let me know.