I get a little bit of an immediate hangover a couple hours after dosing oxycodone, sometimes resulting in a headache but usually only a stomach ache. It pales in comparison to the hangover I get from hydrocodone... More powerful opioids don't cause me any problems even after large doses.
I can't help you with feeling tired, other than suggesting you use your last daily dose earlier in the evening. We process drugs more slowly when we go to sleep under their influence. I can help with the stomach ache, though. Always eat after taking oxy, if you do it a couple hours in, or if you'd rather wait for the effects to completely wear off and just have a snack before bed. Whenever I feel a stomach ache coming on during an opioid's effects or directly after, I eat 100-300 calories and all nausea and cramping is immediately alleviated.