Re: Blood in expressed milk.
I would also call Medela first, they may be able to talk you through some troubleshooting over the phone. I called them once when I lost suction, and they were able to walk me through to get it working again.
I got blood in my expressed milk once when my little guy bit me the night before. Even a little trauma can cause blood. Sometimes the baby's saliva can change when they are teething (or when they are starting new foods), which can damage nipple tissue.
I called my lactation consultant about it when it happened to me, and she said that the milk was fine to give my little man (because that's what he would have gotten if he were on the breast). She wasn't sure about freezing it and then re-using, but freshly expressed was just fine in her opinion.