I have a small lump on my manubrium that has been causing pain off and on for the past few weeks w/ deep breaths and arm movement. pulled muscle?

Costochondritis: Usually a pulled muscle doesn't last for weeks, so it may something else such as costochondritis, especially if the lump is on the side of the manubrium where one of the ribs attaches. It hurts when you breathe or move your arms. Gets better on its own over time, but ibuprofen can ease the discomfort.

Medical check up: If your pain is persistent for more than 3 weeks or if it is getting worse, you need to get a check up from your family Doctor or PCP. Any lump on a bone has to be taken seriously, especially if it is growing in size or if it is causing pain. You may need some X-rays done after the doctor has done a physical examination of this swelling. Good luck.

That one really: needs to be looked at directly. Duration of symptoms, your demographics and an in person physical exam are needed before anyone can even begin to develop a list of possibilities.