Is Bone Grafting done immediately after the infected tooth is extracted?

Yes, ideally you want to have bone placed into the extraction socket at the same time as the extraction. This minimizes the number of surgical interventions and lowers the cost. As well, placing the bone graft at the time of extraction allows for better manipulation of the site to ensure a wider ridge that will hold the implant four months down the road. 

We usually bone graft all of our extraction sockets at time of extraction.  The use of the ND/YAG laser has changed the dynamics of the healing time frame and the quality of the bone.  We use  techniques that keeps the tissue instead of removing all the tissue as we were taught in dental school. This concept with the laser has changed the dynamics of surgery.

It depends on a few things and the intent of the grafting procedure.  If it is to maintain the width of bone from the extracted area for future implant placement, the area can be adequately cleaned and graft material placed.  It is typical to wait longer before placing an implant in this situation however.  If the intent is to create additional width of bone, usually the area should heal first.  There are alot of different opinions on this subject, but if the periodontist you are seeing has experience in this area, defer to their judgement at the time of extraction. 

Every Situation is different.  Every surgeon has their comfort zone as well.  Infection in the extraction site is not a definitive contraindication for delayed bone graft.  I routinely graft the socket of extracted teeth even if there is some infection present.  The extraction site is prepared appropriately removing all infection until clean, the socket is then grafted using bone and an appropriate membrane if necessary.  The 'Pimple" you describe could mean there is a "hole" in the bone in that region where pus was draining.  this tissue needs to be removed and a membrane placed between the graft and surrounding tissue in order for it to heal.  The time of extraction is the best bet to get a good grafting result, otherwise a much more significant graft will need to be done prior to implant placement.  This is based on my experience only, but I have performed it several thousand times.  I would NOT place an immediate implant in an infected site though.  Grafts will heal as long as done correctly, but an implant will get infected about 50% of the time.In my office you most likely would have the graft done then delay the implant for 3-4 months 

If there is active infection the day of the extraction, then you will NOT be able to have grafting done the same day. I would imagine the periodontist or oral surgeon would want you to be on antibiotics at least 3 or 4 days prior to the extraction. Ask your surgeon these questions.