|The same thing has happened to me a few times now within the last 18 months.
It is not "in your system". You have to find the source. You do not have to come in direct contact with the plant. It could be in some clothing you wear. Hunters sometimes get poison ivy every hunting season. It is from their coats that were never washed.
I got it from logs delivered by a tree service. They had no vines on them, but most likely had the "poison" oil. It can stick around for 5 years. You cannot see it. It could be on a hand rail in our house. It could be on your garden tools, rake, shovel etc..... Think about it and look for the sources. Clean them with detergent. The rash will not come back it you do not come in contact with the cause.