Allergies often don't show up until the allergen reaches a certain threshhold in your system. I took penicillin as a kid and several times as an adult. It wasn't until about a year ago that I had a horrible allergic reaction to it. The doctors told me that this is common with allergies. In small amounts, over time, you are ok, but at some point, your body just can't take any more of the allergen and it reacts.
Also, I think the nurse was being very insensitive. Because you still have a detectable amount of HCG, you are "technically" pregnant. They will likely monitor your level for a few weeks. Once it's undetectable, your body will be ready to try again. Every body is different. After a m/c at 10 weeks and a d&c, I was told it could take a few weeks to a few months. I think it took almost 7 weeks.
Sorry you are going through this. I hope you are on the road to healing physically and emotionially from this loss.