Something fierce
Definition 1 of 1
Pro Tip 1/3Emotional Intensity
Used to express a strong emotional response or feeling. 
When she left, I felt lonely something fierce.
Pro Tip 2/3Regional Flavor
It's a regional expression common in North America, may not be understood elsewhere. 
He was craving that pie something fierce.
Pro Tip 3/3Informal Speech
The phrase is casual and might not be suitable for formal contexts. 
This headache is bothering me something fierce.