There isn't a clear, linear answer to this question.
Attempting to conceive can be extremely stressful. It can even take a toll on a woman's mental health. So, it makes sense that researchers in 2011 examined whether emotional distress in women attempting to conceive is associated with their failure or success to become pregnant. Luckily, the study found that high levels of anxiety experienced by women before undergoing IVF treatment did not affect their results negatively. The research study's conclusion stated that, "The findings of this meta-analysis should reassure women and doctors that emotional distress caused by fertility problems or other life events co-occurring with treatment will not compromise the chance of becoming pregnant."
According to Dr. Alyssa Dweck, you can miss you period due to stress. Dr. Dweck went on to explain to Women's Health that "this particular area of the brain, the hypothalamus, is where a lot of the hormones for your period are regulated," and that the hypothalamus is affected by stress. So, stress may have some impact on the process of attempting to conceive. However, researchers still do not have a definite answer as to whether one's mental health has a negative impact on their ability to become pregnant. Even then, common side effects of stress such as fatigue or a change in one's sex drive can affect low long it takes a woman to conceive.
While there is no confirmation as to whether stress can lower one's chances of becoming pregnant, it is widely known that infertility can have a grave effect on one's mental health. Side effects include depression and anxiety. To manage your stress, it is important to reach out to loved ones and even mental health care workers during this stressful time. Journaling may also help. Practicing self-care habits to nurture your mental health will help in the long run, such as for when you do become pregnant. The overall message is to take care of your mental health. Doing so will benefit both you and your future child in the long run.