Hello,
Thank you for contacting us at "Ask a Doctor". I will try to answer your questions the best of my ability.
I have reviewed your questions, and it is certainly possible that you have a so-called 
costochondritis.  The other possibility would be a simple 
intercostal muscle strain in the same region.  If you not have any swelling present then this is very unlikely to be something like a 
hernia.  Also, 
spleen problems do not present in this way, and so this would also be very unlikely.
I think at this time it will be sensible to avoid any lifting.  You can certainly take over-the-counter remedies such as 
ibuprofen or 
Tylenol if it is particularly painful.  A local application of ice in the form of a bag of crushed ice applied for about 10 min. 4 or 5 times a day, would certainly help.  I would continue with this approach for the next 5-7 days.  If after this time, your symptoms are worse or you have developed any new symptoms I would certainly consult with your 
primary care physician.  At this time I do not see the need for further tests or x-rays, et cetera.  I feel confident that this condition will settle in due course.
I hope this information is helpful.  Please not hesitate to contact me again if you have any further questions.
Best wishes,
Adrian Rawlinson, M.D.