Hydrogel buttocks injections are a lot less invasive and more affordable than buttocks implants.
Despite this benefit, it is still considered a cosmetic surgery and you should take special care after the injections.
After the injections-What to Expect Even though it is an injection that will get your butt to the size you want, you need to take the same precautions as if it were a typical surgery.
Unfortunately, this particular form of surgery is often done on the black market by unlicensed people and can have disastrous results if not researched properly.
You need to make absolutely sure you see a doctor that is board certified and do all necessary research.
As with any surgery, there will be discomfort, so some things you can expect are:

• Area of injection will be swollen, red and sore for about 48 hours.
  
• Some areas may seem larger than others, this is to be expected and will even out in about 2 weeks
• May be a small amount of seepage of the Hydrogel in areas where injected
• Swelling of the injected sites will decrease after 2 days; additional Hydrogel touch ups may be needed
• Expect some decrease in volume, size and projections
• Final results will be seen after about 1 month
• You should expect to see minor stretch marks due to the increase in size of the buttocks with Hydrogel

Instructions for Hydrogel Procedure

• Begin taking the antibiotics prescribed the day before your procedure, continue for 6 days after or directed by your doctor
• After the injections, when you shower disinfect the area and place gauze over the injection sites on the buttocks

Do's & Don'ts

• Do not sleep on your back for 24 hours after the procedure.
  Sleep on your stomach or side
• Do not sit down for long periods of time, get up often and walk around
• Do not take super hot or very cold baths or showers
• Do not put ice or hot packs on the area
• Do not have sex for the first 48 hours, and do not perform excessive exercise
• DO walk around in air conditioned areas
• DO take anti-inflammatory medicine for the first 4 days
• DO work out after the treatment, but keep it at a minimum
• DO massage the injected areas as instructed by your doctor

Always follow your doctor's instruction before and after any surgical or invasive surgery regardless of how minimal it is.
In order to see the full results after your surgery, be patient and expect to wait a few weeks before you see any real results.