Is it safe to take tramadol the same DAY as Benadryl (diphenhydramine)? So if I take Tramadol at like 7am, may I take Benadryl (diphenhydramine) later that evening?

Sleepy. Both medications can make you sleepy, be careful, don't drive or operate any machinery while on these. But they can be taken.
Risk of CNS. depression if taken together, way your options, ask your doctor for an alternative, third generation non-sedating antihistamines as desloratadine, would be an option, ask your doctor about it.