Breastfeeding...do I worry about this?

My 5.5 month old is EBF. At around 2 months she started having small amounts of red blood in her BMs and some mucus, it only happens here and there and has never been consistent. It is never accompanied by any change in behavior (sleeps fine, is happy, etc.). I took her in to see the doctor a few weeks ago because she had multiple diapers with blood and mucus and was told that she did have an anal fissure but that I should eliminate dairy as that could be behind the blood, mucus and be the cause of the fissure. I have had no dairy for 16 days and she just had another BM with blood and mucus. It is obviously something that I am eating, I have been writing down everything that I eat...but it seems like it could be anything (I am more suspicious of tomatoes, strawberries, bananas, pineapple than dairy...things I don't eat daily, but do eat regularly). How aggressively do I try to find the cause? It seems that short of going on a very strict elimination diet, I'll never figure it out, as it is pretty infrequent/inconsistent. If that is what needs to be done, I'll do it... The only reason I question what I should do is that she is growing well and is perfectly happy and content and she is the type of baby who'd let you know otherwise.