When a woman is pregnant, she might experience missed periods, nausea, and being constantly tired. However, stress can also bring these signs. Sometimes getting tested one week after intercourse may not give accurate results. If you want to be more certain, wait longer and do another test. 

As per the symptoms listed, an individual is likely to be having irregular periods. This can be attributed to hormonal imbalances, stress, or even weight changes. It is important to consult a gynecologist to establish the cause and then get the right treatment.
 

Changes in menstrual blood flow can be influenced by various factors, including hormonal imbalances, medications, stress, changes in weight, or underlying health conditions. Since you mentioned using medications for skin allergy,

Plan B is most effective when used as soon as possible after unprotected sex — preferably within 72 hours. It prevents pregnancy by postponing ovulation. However, it is essential to remember that it is not 100% effective. If you miss your period or notice any unusual symptoms, make sure to take a pregnancy test. 

In cases where a girl has not engaged in any sexual activities or masturbation before the age of 20, she might experience a sensation of tightness in her hymen when she attempts to have sex. The hymen supplies a faint tear, therefore, the possibility that in the course of having physical intimacy, it does not stretch greatly could surface. Nevertheless, it's completely normal, and thus no need for concern. 

Yes, methotrexate abortion can have side effects such as nausea, vomiting, and abdominal pain.

It is normal for girls to not have­ their period some time­s. The big reason is often change­s in hormones. Stress, losing or gaining weight fast, and too much e­xercise can all cause misse­d periods. Living a healthy life and not be­ing stressed can help. If you are­ worried, it is good to talk to someone you trust, like­ a parent or the nurse at school.