Thanks everyone for the well wishes.  We did get to the vet today and saw, the wonderful Dr. Jim who was the doc who diagnosed McGwire's cancer initially.  He looked him over really well, and said he was very impressed with how well he was doing!?!!   McGwire's weight was good, not losing any weight, though his muscle mass is down certainly.  His heart and lungs (!!!) sounded good.  His lymph nodes on his rear legs were normal and even in size, despite the lump.  At the time of the visit, he was moving well, wagging his tail, sitting down and getting up from that.  So...

The "diagnosis" was that McGwire pulled something or aggravated something in his back during the snow storm and since he can't compensate for that well, it really affected him.  We are to keep with the deramaxx another day or two, and if he continues to improve, then to continue it for a week, but if he's still in pain in a day, then we'll add tramadol. 

In more good news was that Dr. Jim agreed with our decision not to remove the lump initially or now. (We'd seen Dr. Mark for that issue whose initial reaction was to cut it out, but when we decided not to, he was supportive and understanding.)  Obviously, it's a concern, but taking it off, in his opinion, would have been much worse because the would have had to take such large margins, dug deep, and since it's on his amp side, it would only cause Mac mobility issues. 

I also mentioned that we hadn't gotten lung x-rays since November and asked if it would be a good idea to do that or to spend that money on treats, and he said save it for the treats.  His lungs sounded good and he's showing no signs of issues so we went to petsmart and got a big bag of yummy (grain free ) treats! 

Sorry for the scare, and I really was scared, but all the good thoughts definitely have helped!!!