This warm sensation is called as paresthesia. This can be due to pinched nerves in the back. People who sit for long hours are prone to it. With your known medical issue of thoracic and cervical bulging discs, it is further likely that you have bulging disc in lower back too (lumbar region). Following investigations would be required to confirm the cause;
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) Electrotherapy like trans cutaneous electrical nerve stimulation: done by physical therapist. Other thing are electrical stimulation, phonophoresis, iontophoresis, relaxation, and biofeedback.
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) Lumbosacral corset or support or brace
5) If obese or over weight, reduce weight for long term benefit.
6) Epidural steroid shots
7) Surgery is usually last resort, when the above conservative measures fail. 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).
This is a slide show for the exercises (you can pick up your own set, which suits you);
You can consult following specialists (apart from your GP);
b) MD in Physical medicine and rehabilitation
Please feel free for your follow up questions.