The off and on hot sensation is termed as paresthesia. The common causes are;
1) Pinched nerves in back
2) Vitamin B12 deficiency; a blood work for B12 estimation is done.
3) Diabetes; Glucose tolerance test and glycosylated hemoglobin are done.
With your back pain, this is most likely due to pinched nerve in back. This can be due to;
1) Herniated/degenerated disc in back
2) Lumbar spondylosis; bone spurs in the back vertebrae pressing on the nerves.
Following investigations would be required;
1) X-ray of the lower back
2) MRI of the spine
3) Nerve conduction velocity (NCV) study
4) Electromyography (EMG)
Following measures would be helpful;
1) Back care in the activities of daily living;
a) Avoid activities which increases the pain.
b) Rest intermittently
c) Avoid bending at 90 degrees
d) Pushing and pulling should be avoided till pain subsides
f) Avoid prolonged sitting and standing
g) Avoid sitting or sleeping on floor
2) Anti-inflammatory analgesics like ibuprofen, other analgesics and muscle relaxants
3) Good supervised physiotherapy: The exercises consist of abdominal bracing, modified sit-ups, double-knee-to-chest or low back stretches, seat lifts, mountain and sag exercises, knee-to-elbow exercises, hamstring stretches, extension exercises, and extension flexibility exercises. Swimming exercises (pool exercises) are best for back pain. Initial stretching and later strengthening exercises are taught.
4) Reduce weight for long term benefit.
You can start the following exercises;
1) Straight leg raising: Lie on the bed with your back and remain in a relaxed position. Slowly raise one of your legs upward and keep it as straight as possible. Count up to ten, and slowly bring down the leg. Do the same with the other leg. Repeat this exercise ten times.
2) Curl ups; lie on the back with knees bent, fold arms across the chest, tilt the pelvis to flatten the back, and curl-up lifting the head and shoulders from the bed / couch. Hold for ten seconds, then slowly lower to starting position. As strength builds, aim to complete one sets of ten curls. The exercise should be done twice a day (both the sets).
Please feel free for your follow up questions.
I would be happy to assist your further, if you need any more information.