Had a scare yesterday with my son...

Maggie • 25🌞Mommy to💙Luca 12/31/13💙 Logan 02/14/17💙
He's 1 (23 months) and we are working on getting tubes in his ears for recurrent ear infections and hearing issues due to fluid.
   ---Saturday night his gums were kind of red and he had a slight fever (99 F) so I gave him Motrin and he went to sleep.
---Sunday morning he woke up and his gums were swollen and his fever had gotten worse so we took him to the ER. They told us it was a double ear infection, prescribed Antibiotics, and sent us home.
---Monday (yesterday) I called his Pediatrican as soon as they opened to ask if I could bring him in because of his gums; I told them the hospital had no idea. They said take him back right away; he needs blood work and other tests.
  As I woke him up he would not stand or walk, his gums were bleeding, and he was vomiting.
     When we got to the ER they gave him an IV, gave him Zofran for nausea, did X-rays, ordered a million blood tests and urine tests. The doctor asked about my family history about childhood cancer, blood cancer/disorders etc. I told him as far as I know we don't have those in our history. 
The tests came back good, his platelet counts are good, but his RSV test was positive and he does also have the double ear infection.
I'm so worried still about the fact the "C" word was brought up. I know his tests came back fine but I can't shake it... 
Has anyone had experience with this? Should I seek a second opinion just in case or do you think we're fine?