I've pulled things, cracked bones, strained backs etc but last Thursday I had a new one and I'm not able to figure out just what happened.

I was picking up a large landscaping pot to empty it into the wheelbarrow when something in my right bicep popped. It did not make a noise, just a short sharp pain. I was able to complete the transfer of the pot into the wheelbarrow but decided I would call it a day and see how the arm behaved. It continued to ache long enough for me to call my PCP and find out he was out of town. I got his backups name and number, put an icepack on the arm and sit down with a cool drink. I ended up going back out with the wife, putting all the tools and stuff away and relaxed with some Netflix.
On Friday it was somewhat sore when I got up, got to feeling well enough for me to unpack her new VegTrug and get it mostly assembled. By near bedtime it was showing some yellow 'bruising' across the middle of the bicep and was hurting again so a Tylenol, an ice pack and bed. By today I was experimenting on what I could do and what would cause pain. Carrying a gallon jug of milk with the arm straight down was not at all comfortable but I could wrap my arm around it and not cause any pain.

Now my question: muscle tear? tendon sprain? ligament? Your best guess?