Hi jacqui32, the only advice I can give you is to keep on trying. 4 months isn't that long of a wait most fertile couples take up to six months to get pregnant.
As far as any tips, I have tried them all, i've tried geritol, green tea, robitussin, carrots, grapefruit juice, epo, the pillow under the hips and not moving until morning, missionary position, bding everyother day, bding every day (tiresome), I have tried just about everything and I am now on my 7th month of trying and no luck so far. Try not to put too much stock in certain methods cause they work for some and not for others.
So keep on trying, it will happen.