MUMIRZA, No gel or pill can increase your penis size, just like she cannot decrease her vagina size or looseness. If you have money to waste, rather donate it to a charity of your choice.
It sounds like she is unhappy with her sex life. Ask her to show you how she makes herself orgasm. Try doggy or her on top of you and stick your hand down there and rub her clitoris while you are having sex, try bringing some excitement and variety back into your sex life, try a new position, try extended foreplay before sticking your penis in, get a book on sexual techniques, get a small vibrator and use it on her clitoris during intercourse. If she wants to feel filled up, buy a large dildo and use it while giving her oral sex or fingering her clitoris.