Taking my carbamaziapine after taking a Benadryl?

There is a moderate interaction between both medications, moderate meaning:

Moderate Moderately clinically significant. Usually avoid combinations; use it only under special circumstances.

Interactions between your drugs
Moderate
carBAMazepine diphenhydrAMINE
Applies to: carbamazepine, Benadryl (diphenhydramine)

Using carBAMazepine together with diphenhydrAMINE may increase side effects such as dizziness, drowsiness, confusion, and difficulty concentrating. Some people, especially the elderly, may also experience impairment in thinking, judgment, and motor coordination. You should avoid or limit the use of alcohol while being treated with these medications. Also avoid activities requiring mental alertness such as driving or operating hazardous machinery until you know how the medications affect you. Talk to your doctor if you have any questions or concerns. It is important to tell your doctor about all other medications you use, including vitamins and herbs. Do not stop using any medications without first talking to your doctor.

Source and more info: https://www.drugs.com/interactions-check.php?drug_list=896-1617,497-0

Do speak to your Dr. about this potential interaction.