I don’t know why my tomatoes leaves are droopy

As the title say, my tomatoes leaves have been drooping and I don't know what I can do to help them.

I water them every 2/3 days when the soil at the top is dry (around 1/2 L of water). They have plenty of direct sun from 9h to at least 18h. They are planted in at least 5 gallons pots and have been fertilize with a slow release fertilizer. The potting soil is a special mix for container gardening and we have added perlite to help the soil retain moisture and to prevent it to be compact.

I saw what seemed to be aphids but I crushed them one by one on each leafs and I check my plant every day, morning and evening.

But, my tomatoes leaves are still droopy and are curling down and I don't know if it's because they are diseased or is it because they are just like that. Either way, they are still growing very fast and are producing new green leaves.

Is there anything I can do to help them ?