You can use either. from the excursion = the excursion made you tired after the excursion = afterwards

It depends what you want to emphasize with your statement. 'from' emphasizes the effect of the excursion and it being the cause of being tired. 'after' refers to the exact time of tiredness. You could also say: "I was very tired OF this excursion" It also emphasizes the cause of tiredness ,the excursion.