Kitten got an abscess?

I adopted a kitten two weeks ago and the day I got him he had all his shots and got nuetered. He came home and was loopy for a day and a half or so and then as he started to adjust and start running around he then became very sleepy for a few days. All he would do would eat and then go right back to sleep. I... show more I adopted a kitten two weeks ago and the day I got him he had all his shots and got nuetered. He came home and was loopy for a day and a half or so and then as he started to adjust and start running around he then became very sleepy for a few days. All he would do would eat and then go right back to sleep. I thought was odd but he is a baby. But then after about the 4th day I started to think he was sick or something.
So the next evening he had a giant abscess on his stomach between his back two legs that burst. There was lots of puss almost a cup and there was some blood too. It was already after 5 o clock on a Friday so we looked up so info kept it clean, cleaned everything and kept the wound open for at least 2 days. He started to act fine again he isn t sleeping and he is running around like normal playing but I noticed the area got hard where it had drained. We drenched the scab to open it up and no puss and nothing came out but it is tender to the kitten.
1. Im not Sure where the abscess came from because he has been with us and hasn t had any open wounds.
2. Do you think it s healing and we should leave it alone, or should we call the shelter where I adopted him from?
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