4 month shots...

Lucas got his 4 month shots yesterday afternoon. He was already a little under the weather... he woke up Friday morning sounding congested in his nose. I had concerns about him getting immunized with a possible cold, but Dr. Lisa assured us that even if it was a little viral infection, it was safe to go ahead with the shots. He was in such a good mood, until the first needle (the big sad lip poked out) and full fledged screaming ensued after the second shot. It is so hard to watch him in pain. We got home and got comfy in our pjs while David did our weekly grocery shopping (thank you!). Lucas seemed to be doing alright, just drowsy from the Tylenol and still congested. He went to bed at his normal time, around 9... but he woke up not feeling well at 11. No fever, just fussy. I cuddled him back to sleep, but then he woke up again at 1. This time, I knew he had a fever as soon as I touched his little body. He was burning up! His fever was 102.7! It scared the living daylights out of me. I couldn't get the Tylenol in him and strip his clothes off fast enough. I called for David to help, too.. he got us a cool cloth and we began the cooling process. The fever started coming down, but took about 2 hours before Lucas was comfortable enough to fall back asleep (fever back down in the 100-100.9 range). After that, David and I alternated getting up every hour checking on our sick little angel. We also alternated the Tylenol and Baby Motrin every 2 hours. That kept the fever down for the rest of the night, and this morning we thought we were out of the woods except for his sniffles and congestion, but around 2 this afternoon the fever returned. Looks like it might be another long evening... Does anyone know how long this should last?