Filtering data on the dataset using the same dataset for subquery filtering

I am having trouble writing exactly 4 queries in mysql.

Here is the view I am using for queries: http://pastie.org/8403299

Here is the Raw Data you can check
goo.gl/z7Vv9X

which you can check.

What is needed:

1) Gained students are those who exist in the selected / filtered month and don't exist in the previous month.

2) Lost students are those who exist in the previous month of the selected / filtered month and don't exist in the selected / filtered month.

3) Get a list of all lost students since the start of the center till now().

4) Get a list of all gained students since the start of center till now.

I am currently stuck with query 1) (Gained students are those who exist in the selected / filtered month and don't exist in the previous month.)

I have written it like that (see just below), but I get the same number of rows back if I haven't filtered anything... uff.

SELECT *
FROM lessons_master_001 my1
WHERE NOT EXISTS
(
SELECT 0
FROM lessons_master_001 my2
WHERE
my1.student_id = my2.`student_id`
AND
my1.teacher_id = my2.teacher_id
AND
my1.`student_payment_id`= my2.`student_payment_id`AND
CONCAT(CAST(MONTH(DATE_ADD(my1.Lesson_Booking_Date, INTERVAL -1 MONTH))AS CHAR(20)),CAST(YEAR(DATE_ADD(my1.Lesson_Booking_Date, INTERVAL -1 MONTH))AS CHAR(20)))
=
CONCAT(CAST(MONTH(my2.`Lesson_Booking_Date`)AS CHAR(20)),CAST(YEAR(my2.`Lesson_Booking_Date`)AS CHAR(20)))
)

PHP:

My logic is like this so I take everything from the view lessons_master_001 and give alias my1 and in the NOT EXISTS clause I am giving to the same dataset alias my2, then join those ID's that are also used in view lessons_master_001 and then try to connect previous month from data set my1 with current month from data set my2.

I am using DATE_ADD function to subtract month from current date and practically get date - 1 month.

I would really appreciate any help you will provide, cause I lost 2 days already on it with no progress in front.

Thank you in advance.