During this phase the body is preparing for a potential pregnancy

Day 1 is when bleeding starts:

• The bleeding is a result of the body shedding the old, thickened lining of the uterus. 
• Bleeding can last 3 to 7 days, and may be accompanied by the following symptoms
  1. Cramping  - causing the uterus lining to be shed
     • Breast tenderness
       • According to NHS UK, the symptoms of breast pain includes
       • a dull, heavy or aching pain
       • the pain can begin up to 2 weeks before a period starts and will usually worsen and then disappear when the period end
       • can affect both breasts with pain spreading to the armpit
  2. Before starting a period, many women will experience back pain or cramping with bloating.
     • If these symotoms follow a predictable pattern and don't cause severe problems, its usually nothing to worry about
  3. Goes hand in hand - that feeling of irritability can easily lead to to anger or experiencing a rollercoaster of emotions in a short period of time.
  4. Experiencing heavy bleeding at the start of the cycle often causes tiredness, which is normal due to the decrease in oestrogen levels and therefore leading to tension type headaches or migraines 

• Early in the follicular phase, the follicle stimulating hormone (FSH) and luteinising hormone (LH) levels start to increase, stimulating several follicles in the ovaries. Each follicle contains a single egg.
• As the follicles develop they release oestrogen, causing FSH levels to fall, inhibiting any further follicles from being stimulated.
• Usually only one egg will fully mature and cause a surge in oestrogen, initiating the thickening of the endometrial lining.
• Oestrogen levels rise dramatically the days before ovulation, peaking a couple of days before the next phase begins.