how and what to hump?

Instead try using a brush or a toothbrush or anything that vibrates

Also, if you don't have anything that vibrates, try puting a pillow between you legs and rock your pelvis forward and backwards. This will put steady pressure on your clitoris and will give you lots of pleasure. Experiment with different rocking directions and different objects such as the edge of your bed or the side of the bath. Make sure everything you do is comfortable and doesn't hurt. Also if you decide to insert anything into your vagina, make sure its clean. I hope I helped, thank you!