I think that 1.3 is very low...especially since they want you to be 2.5-3.5 but in the beginning it is very difficult for them to prescribe the right amount of coumadin, since everyone is different. For the first couple weeks, maybe even first couple months, your levels will jump around pretty quickly. Well, at least they did for me. It is true that pretty much everything effects your INR. The best thing to do is just get it checked frequently, until it starts evening itself out. Usually they will have you come in once a week, then when your in range for awhile, they usually have you come in once every two or three weeks. Especially since your still recovering, your body isn't back to "normal" yet. I'm sure your not eating what you usually do, or excercising like you would.
All I can advise is just to get checked regularly. I know I had been 3.0 for a very long time, which I was so proud of. Then one day I went in, and I was about 1.7
I couldn't believe it, I thought back to was it something I ate or something I did...maybe I missed a pill?? I couldn't think of anything, but my cardio said sometimes it just happens. So bottom line, just make sure you listen to your docs, take your meds, and get checked. Good luck to you and hope your recovery goes well