T cells, which are one type of white blood cell in the immune system, somehow become sensitized to proteins in the CNS. When T cells become activated, they enter the CNS through blood vessels and produce damaging inflammation.
1 Fatigue or Tiredness: Feeling fatigued or more tired than usual, is a pregnancy symptom which can also start as early as the first week after conception.  Morning Sickness or Nausea: This well-known pregnancy symptom will oftentimes show up between 2-8 weeks after conception.
Some of the most common causes of constant nausea include pregnancy, food consumption and stress. One of the most recognizable causes of nausea is pregnancy. In fact, it is often the first symptom that a woman experiences and can occur within a few weeks of pregnancy. Constant nausea, or morning sickness as it is frequently referred to, can strike pregnant women at any time of day.