Hi, I was on Avastin myself for 6 months (along with Folfox). Not to scare you, but definitely contact the Dr. right away because Avastin has a very rare side effect of causing a perforated bowel. I certainly hope and pray this is not the cause of his bleeding, but you definitely need to check it out. The bleeding certainly could be as simple as hemorroids from straining while constipated, perhaps- but please have them check it out right away. I would get constipated the first couple of days after Avastin infusions, but I don't think the constipation was from the Avastin- it was from the antinausea meds they ran into me each time. It was usually 2-3 days of constipation, then I'd have a couple of days of diarrhea to follow. I'd have actually a couple of days of normal bowel movements right before I'd start the process all over again (every two weeks). I didn't have any colon surgery, though, so what's normal for me may be quite different for your husband.
The only big side effect I had from Avastin was high blood pressure, which I went on medication for- it controlled it some, but it was still high. Now, 3 months later, my blood pressure has returned to what it was before I ever started chemo.
Best wishes and prayers,
Lisa