Is there a way of definitely having a girl the next time I get pregnant?

Unfortunately, there are only suggestions and tips you can follow, but no 100% guarantee you'll get a girl. You could try the Shettles method, which claims that having sex 2 to 4 days before ovulation has a higher chance of producing a girl. Other methods include eating more vegetables, having a hot bath before doing the deed, doing the deed in missionary position and others. http://www.bellybelly.com.au/conception/how-to-conceive-a-girl/