You are more likely than not shaving either against or across the grain.
If you have some growth, feel free to send over some clear close up pics to email@example.com. We'd be happy to map out your grain for you. Be sure to include images of each area that needs mapping. We'll send images back with arrows showing you the direction to shave in. It's important that the images are clear, close-up, in good lighting and that the hairs are long enough to see, but not too long that they start to curl.
If you are shaving against the grain, or even across the grain, you cut the hairs beneath the skin and they grow back into it, instead of straight out the follicle. If you grain isn't mapped properly, we'll need to get this done before you shave again.
The other way bumps are formed is by not shaving often enough. We recommend shaving either daily or every other day to prevent new hair growth from curling and growing into your skin.
Glide the long edge of a credit card along your skin to see in which direction your are pulling the hair up, and which one you are laying it down. The direction in which you are lifting the hairs is against the grain, and the direction in which you are laying it down is with the grain. We strongly encourage only shaving with the grain.