mid back pain that wakes me up

i am a 22 year old male currently working for UPS, and about 2 months after working with them, i started to get this mid back pain that wakes me up after 3-5 hours of sleep.
i think i know what caused it, but i'm not certain. i deliver to a mall, and i lifted something that weight approx. 10-20 pounds (this was about a week or 2 before i started waking up from back pain). because the store was narrow, i twisted my back without even thinking. right after that, my upper back killed for the rest of the day.
advil extra strength (400 mg of ibuprofen) was the first thing i tried. it seemed to help and i could fall back asleep after 20-30 min. however, after the first week of taking advil everytime i woke up, i started to feel the pain again when i tried to go back to sleep. i didn't like the idea of taking advil every day, so i stopped.
i went to the doctors and he said it wasnt anything serious. all he did was felt my back. made me do some stretches, and told me to do pilates when i go home. its been a month since that appointment, and i've only done the pilates 4 times, 4 days in a row. i didnt notice much of a difference, and maybe i gave up too fast on it.
i also soak in a hot bath with epsom salts. i've tried hot/cold packs for about 20 minutes at night. i still wake up. also tried bengay, and it seemed to work at first, but after a week of using it, it didnt seem to work as well.

lately, i realized that i used to pull my hand cart with my right side(for about 2 months). most of the loads were really heavy. most of the time, the pain is in the middle of the mid back, or on the right side. after pulling with both hands now, once in a while my left side will hurt too, and now maybe 5-6 times a day, a muscle by my left rib will twitch once.

lately, the pain hasnt been so severe.  last night was brutal though, i woke up every 2 hours. the only difference i can think of is that that day i had 3 coffees. can coffee make muscles tense and spasm?

the only comfortable position for me to sleep is on my side, and my spine twisted. this is how i have always slept, even as a kid. since this pain has started, i've been trying to sleep on my back, and when i do, i still experience it the pain.

should i give pilates another chance? or should i just be relaxing when i get home from work?
should i take advil everyday?
if i take advil, should it be everytime i feel it? or should it be on a set schedule? like, does advil actually permanently fix these spasms if i take it like 2 or 3 times a day?

[atdi198d]

i should have mentioned that i rarely feel this mid back pain during the day. it naturally goes away if i get up and walk around, or sit in a chair.