Periods occur when a girl reaches puberty. Sometimes, the periods can be irregular or painful. This may be because of stress, a poor diet, lack of sleep, or health problems. For example, some of the things she can do are eating well, exercising, and learning to relax. The excruciating discomfort can be unbearable without a doctor's advice.

Normally, implantation bleeding is lighter and shorter compared to the usual menstruation flow. A negative HCG test could mean that it’s not a case of pregnancy. The tests may have been carried out too soon for the existence of any pregnancy to be detected. 25 days may also be too soon for an ultrasound. So it's either way too early for these tests or the likelihood is that you are not pregnant. Keep an eye on the symptoms and repeat the test after a week or two for better results.

You didn't mention the pregnancy test and also even if it is possitive, you need to see your gynecologist. They can ask for some tests and confirm about pregnancy or any other health conditions
 

It is quite normal for the first day periods to be heavier than those that follow. The explanation for this is that the endometrial lining of the uterus completely sheds on day one resulting in heavy menstrual flow. With every day the amount of shedding reduces reducing to a lighter flow. Nevertheless, should you develop unusual heavy bleeding or uncommonly long periods of menstrual flows visited a gynecologist for the assessment and treatment.

Vaginal dryness can often be encountered and it may have different causes like menopause, hormonal changes, stress and anxiety, medications or allergies. It is recommended to find a gynecologist or an expert on sexual health who can address your concerns. 

This could be due to HORMONAL IMBALANCE or STRESS.. Consult a gynecologist....