The bump started off very small and has grown more rapidly in the last day or so.
It sounds like your puppy has developed a pus-filled abscess on its underbelly and groin area, which can result from bacterial infections, parasites, or other skin irritations. Given that it has grown rapidly in the last day, it's important to address it promptly.
At home, you can take the following steps:
First, gently clean the area with a mild antiseptic solution like chlorhexidine or betadine. Avoid using harsh chemicals or alcohol, as these can further irritate the skin.
Next, apply a warm, damp cloth to the bump for about 5-10 minutes a few times a day. This can help the abscess to drain naturally.
It's also important to monitor the bump for any changes in size, color, or if it starts to ooze more pus. Additionally, watch for signs of discomfort in your puppy, such as excessive licking or scratching.
If your puppy is scratching the area, consider using an Elizabethan collar (cone) to prevent further irritation and potential infection.
Given the rapid growth and presence of pus, consulting a veterinarian as soon as possible is crucial. They can provide a more thorough examination and may prescribe antibiotics or other treatments to effectively address the infection. Additionally, the other symptoms you mentioned, such as diarrhea, dry nose and paw pads, and nose whistling, could be related and should be evaluated by a professional.
If you have any further questions, please feel free to ask. Thank you.