What Causes A Swelling At The IV Injection Administration Site?

I was admitted to the emergency room a few months ago they gave me an I.V. And gave me sugar because my blood sugars were low I was dehydrated they gave me fluid for that and my potassium was low. I was released 3 hours later. My hand that the I.v was in still continue s to swell and its is moving to my fingers and they are almost twice the size now. I have no idea why it is swelling. My veins are hard in areas on my hand no red inflammation not much pain just worried about my swelling why this is doing this I went tot the dr for this and the dr said its most likely a small clot is my vein but it s not a major vein so it s not to worry about why is my hand doing this