Good Day To You. Let Me Explain You My Condition.

Good day to you. Let me explain you my condition. I had my last periods on 28 th December and had negative pregnancy results. Later on 5 th April after a blood test I found that I am 4-5 weeks pregnant with 529 mlU/ml. I am interested to know
》why I did not get periods in January and February?
》Will this cause any problem for pregnancy?
》I had few drops of vaginal blood on 6 th Should I be concerned?
Thank you for your help in advance.