I got refusal for PLAB visa

[bringalz]

I applied for PLAB visa and got refusal the cause is :
Your application:you have appied for entry clearance to undertake PLAB Test in the UK for 14 months.I haveconsidered your application under paragraph 75A of UK immirgation rules.

The decision : you state that you are a dcotor at the specialized eye centre with monthly income of RGP 3000( 300 sterlings) .I note that you took up this position very recently
less than a month after you were refused a visa due to concerns that your income has been exaggerated.There is no evidence of the origin of EGP 100.000 (10.000 STERLINGS) deposited in your account in one lump sum. this equates to 33 times your current monthly income.your previous monthly income was even lower and so i am not satisfied these funds are available for your exclusive use.
this also leads me to doubt your intentions.therefore i am not satisfied that you meet the requirements of paragraph 75A (iii) and (iv)

I want to clarify some points :
1- I mentioneed in my application that I will stay 14 days.. and I have a copy for the application (not 14 months)
2-I changed my job recently ths is because if a better income...so is it better to be in the new posotion for many months to prove that???!!!
3-the one lump sum... I gave them my mother bank statement(stating the amount and the date of transaction which is the same as mine )
and birth certificate in the 1st time I applied thinking that they keep it in my file ...

is that enough to prove that she sponsor me? or I have heard about written concent from should be done and stamped too stating that she will pay all my expenses for my all trip for the exam??

thank you