What happens if you pop a mosquito bite?

You increase the: Potential for infection.

Usually gets worse.: There is nothing to "pop" - that is, there is nothing inside, unless the bite is secondarily infected. Even then, popping it will only worsen the inflammation and increase the chance that it will get even more infected. Leave it alone, or rub a bit of Hydrocortisone cream on it. If it persists or worsens, see your doctor.

It may ^ risk: for developing an infection.

Bleeds: Not much other than a bit of blood. It can get infected so it is important to keep it clean and covered till it forms a scab and try not to scratch it.