IF with multiple conditions please

I have a spreadsheet in which I have created a credit card statement.  I have managed to get most functions to work but an IF function is puzzling me how to get around it and is not coming back with the additional payment correctly resulting in the balance becoming a negative figure.

So, in column:

F is the regular payment,

G with a suggested extra payment,

H with a manual extra payment,

J with the interest paid per month and 

L with the resulting balance

I have IF function that in column G "=IFERROR(IF(L49>F50,L$39,IF(L49<I49,0,L$39)),0)" that returns a suggested extra payment based on column J multiplied by 105%.  This, however, when comes to final payment in column L produces a negative amount.  I have tried to do SUM function with IF and IFS but cannot get it to return the value needed.

I want the IF formula in column G to calculate and return the value suggested in L39 but return the difference between column L and column G when the final balance is less than the regular payment but more than the suggested regular payment.