I Think I May Have Strained A Muscle In My

I think I may have strained a muscle in my chest (at least I hope that's what it is). About 10 days ago, I went on a hayride w/my sons. I am short in height & literally had to pull myself up onto the trailer pulling the hayride...Sort of the way you would pull yourself out of a swimming pool. Most of the weight was on my left side as I pulled my legs onto the trailer. Its hard to describe the exact movement, but its certainly not a movement I use on a daily basis...& there was definitely a great deal of weight placed on my upper left body. I was fine that night. I did not realize there was a problem...I was actually on & off the hayride several times (checking on kids)...so I repeatedly used that weird movement to get on & off the hayride. The next morning I woke up w/upper left chest pain. The pain begins a few inches to the left of my sternum, about armpit height (there is an actual area of tenderness/pain when pressing on it)...pain radiates to just beneath my arm. I can follow a line of tenderness when pressing w/my fingers. No bruising or swelling that I can see (altho, it does feel kind of like bruising) At first, it hurt terribly to bend over (this seems to have improved a bit, but I still have to bend slowly). It also hurts to rotate my shoulder (the pain is not in my actual shoulder, but in the same area as I previously described--across my upper left chest, like a pulling type pain). As I get into bed, I cannot put any weight on my left side or I feel extreme pain. It also hurts a bit to take a deep breath and/or cough (this causes pain mostly in the area closer to my armpit...but does seem to extend over breast toward sternum, as well)--but this has also improved a very slight bit. Overall, its not a constant pain, it just hurts when I move certain ways. (As long as I don't move, don't cough, or take a deep breath, I feel no pain at all...unless I press around my chest w/my fingers & locate the sensitive areas) Like I said, this happened 10 days ago & I have seen minimal improvement. Perhaps I should also note, I have NO problem w/breathing, no heart problems (no family history of heart problems), no persistent cough, etc. To my knowledge, I am an otherwise healthy 36 year old female. Motrin significantly helps, but it worries me because I still have such discomfort 10 days later. I've talked to friends (some nurse friends) who say it sounds like a strained muscle (possible pectoral...or intercostal)...As a single mom w/very limited income, I would really like to get out of paying out of the pocket for a dr visit to be told its a strained muscle & theres nothing they can do. Since the problem became apparent the morning after I did the weird lifting, does it sound muscle related? Maybe a strain? If so, what kind? What about the duration of time...when should the discomfort/pain ease up? How can I take care of it at home? Please advise...I am starting to worry constantly because of the very minimal improvement I have seen over the past 10 days. I can see some improvement, but I guess I would just prefer to to be completely gone by this point.