I often feel sleepy after lunch, and it really had some negative impact on my work. Nap is unfortunately not a choice for me. How can I do?

It may have to do with what you are eating for lunch. Try to avoid heavy carbs and sugar. See if you notice a difference.
Separately, do you get enough sleep at night?

Maybe a few things to consider. If you have already thought of these things…sorry. Best of luck either way!

I think you should look at the kind of food you eat at lunch. Eat more of light foods and include fruits in your lunch. Don't forget to take take water regularly. You should have a routine to keep you alert when you notice the sleep is approaching. Routines like taking a walk.. I hope this helps. Cheers

Okay, soo I'm struggling with the same thing, but I try to give some advice. I usually try to sleep earlier, but if it's not possible try something that will help you feel more awake. Like a cup of coffee, meditate or do some exercise, just a few minutes.

Maybe drink coffee or eat foods that may be energizing, or don't eat foods for lunch that make you drowsy, sleepy or tired, for example, tea, or soup

If you eat too much carbs or a meat then you will feel sleepy. So try to include for green and fruits and nuts in with your lunch

I know that feeling very well. What works for me is a lighter lunch – salads, or veg soups, or a handful of nuts and seeds and an apple, or hummus with celery or carrots. Basically, nothing stodgy, something low on fast carbs. Hydration throughout the day is a key to make sure you don’t overeat during lunch. Filling breakfast will also reduce your lunch hunger making it easier to control the amount you eat. Good sleep and cutting down on caffeine also play a role in energy ups and downs. However, we are humans, and stuff not always goes how we hope even if we ticked all the boxes. I try to schedule concrete and easier tasks for after lunch to build momentum. If I do feel like I cannot muster strength, I do a 10 min breathing exercise (YouTube is good for that) to accept how I feel and move on with compassion to myself as best as I can.

Coffee could be an option. Other two options would be either eat less, so your body won't need as much energy to concentrate on digestion, or skip lunch altogether. Have a protein bar (check the nutrition values) or a simple fruit to give you the sensation of having something in your stomach. You can even have multiple small healthy snacks. Junk food begs for more

If You feel sleepy after lunch the it can be because either your portion is too big or the choice of food does not suit your organism.. if you choose correct portion size and proper food then You will feel energized after lunch. Google about it and try something different next time.
Good luck!

Maybe you can eat less in lunch and split the meal? It can make you sleepy without being hungry, you can reward yourself with fruits &snacks between the meals