If it's the upper left: It's uncommon to experience pain here. When you do, it may suggest a colon, stomach, spleen or pancreas problem. It could also be a pulled muscle as well. Especially since you say it's pain free while laying down. Take Ibuprofen (which will help with pain and inflammation) a heating pad in the area as well. If this doesn't seem to get any better after 24 hours, then do see your doctor so you can be examined.
Hope this helps.
It had only asked to pay again because you had reopened it.. but since you are asking another, I will answer as well here.
Resting is fine.(Everyone is different.. but the standard normal is 40-100, Ideally between 60-90, so you are good there.
It should be maybe around 120-158 (but this depends upon how fit you are.. the more fit you are the lower it should drop. So if you take someone who has been a couch potato for a year.. and then they do some active cardio, they will have a higher rate than someone who has been doing it already.
Hope this makes sense