Generally, about 20 minutes is enough. Maybe your caress and foreplay are not enough! Or she didn't arouse her enthusiasm. If she can reach orgasm, she should feel happy, not tired. You should be able to see her physical quality! It may also be that I didn't adapt at first! But it will get better slowly. Really tired, then don't do it, just caress her body! Do we have to have sex? Emotional communication is multifaceted. If she is tired, you should contact her. Don't let her think that you dislike her for her short time and poor health. Buy her some nutrition! I wish you happiness!