Brief Answer:
Compression of muscle or nerve suspected

Detailed Answer:
Hello XXXX,

Thanks for your query.

Regarding the symptoms as mentioned in your post, kindly let us know about the following:
1. Any recent illness or injury to the back or lower limbs?
2. Is there formation of any swelling or lump in the region which increases with coughing and straining?
3. Sensation of spasm can be secondary to systemic illness. Is there is significant past history or family history of systemic disease like Diabetes, Hypertension, Thyroid disorder, etc. ?
4. Any recent history of Stress, improper nutrition & lack of sleep?
5. Habit of smoking or alcohol consumption?
6. History of prolonged intake of any medication?
7. Any other associated symptoms?

If your answers to the above mentioned questions are "NO" then the symptoms can be attributed to:
1. Compression of muscle due to maintenance of inappropriate posture during sitting or driving.
2. Compression of nerve and blood vessels at the Lumbosacral region.
3. Inadequate hydration status & electrolyte imbalance of the body, or
4. Dietary deficiencies of certain nutrients like Iron, Calcium, Vitamin D, Vitamin B12, Folic acid, etc. which help in blood formation & nerve conduction.

Though application of muscle relaxant gel and massage may provide temporary relief, the underlying cause needs to be treated.
Symptomatic relief can be obtained by intake of nervigenic agents (like Vitamin B6, Vitamin B12, Folic acid) as well as multivitamin & multimineral supplements including iron, calcium & Vitamin D needs to be added in your diet.
Physiotherapy & postural spinal exercise will be helpful.
Also make sure that you avoid lifting of heavy weights or twisting of legs.

If symptoms still persist, kindly consult a Neurologist & get a complete Neurological examination done.
Certain investigations like complete blood count, serum electrolyte estimation, fresh estimation of blood pressure & blood sugar levels, nerve conduction studies and Doppler study of lower limbs will be helpful to rule out any pathological cause for the symptoms.
X ray & MRI of Lumbosacral spine can also be carried out to detect any nerve entrapment.

Wishing you a Good Health.
Please let me know if I need to clarify further.
Take care.

---