Why am I having abdomen cramps? I just drank a liter of calamansi juice in 1 day.

Ohhh that's a lot of calamansi juice in one day, sis! Yes, that could definitely be causing the cramping, the acidity and the sheer volume can upset your stomach, lalo na if your tummy isn't used to that much citrus. A few of us tried doing that "detox" thing with calamansi and same thing happened, so you're not alone. But if the cramps don't settle down in a few hours or if you notice any other symptoms like burning when you pee, best to check with your doctor just to be safe, UTIs can also cause cramping so better to rule it out. For now, drink lots of plain water to help balance things out and maybe stick to smaller amounts of calamansi next time!