Poison oak, ivy, sumac and other "oil" producing plant irritants typically begin irrupting 24-48 hours after contact based on skin sensitivity if you are allergic.
To see pictures of poison oak & ivy and double check your symptoms go to: http://www.rashremedy.com. It also contains an excellent treatment plan.
Tips:
1. To remove plant oils from the skin use a product called "Tec Nu" (spelling may be wrong). Follow the directions carefully. It really works!
2. Make sure you double wash all cloths, towels or bed sheets that may have come in contact with your skin if you suspect poison oak or ivy. You can become easily re-infected with the plant oil that has transfered from your skin to material.