At 20 grams of carbs a day you were doing a ketogenic diet so your body was switching from using carbs for energy to fat and ketones. Some people have a harder time with these adjustments and experience the low carb or keto flu. These people have a time ranging from a couple of days to a week where they feel sick, worn down or like they have the flu as your body adjusts to the lower carbs and changing energy sources.

I've been averaging 200+ carbs a day but started this low carb a week ago and kept to 20-25 a day. I have been feeling weak the longer I do it. Like simple things seem harder, carrying my 3yr old, squatting to pick things up etc. I've upped my carbs to around 55 a day but maybe my "low" is too low? Has anyone else had this happen?

As has been suggested, it's best not to up the carbs right now, but to keep it low.

It's absolutely normal to feel sluggish and/or weak for a little while until you keto-adapt. It gets TREMENDOUSLY better after you have. The "norm" seems to be two to three weeks, but some people can take as much as eight weeks. (I'm pretty sure those who take eight weeks to keto-adapt aren't staying under 30g per day, and/or have their fat/protein intake at a sub-optimum ratio.)

The longer you stay at 20-25g of carbohydrate a day ...and if you can keep your fat intake at around 75% of your calories as a minimum, you'll keto-adapt a little more quickly. If you add more carbohydrate or increase your protein above 20%, it can take longer to keto-adapt. FYI some (especially women) opt for 80% fat and 15% protein and find keto-adaptation comes easier that way.

If you're interested in low-carb for health reasons, stick with it - it DOES get better once you keto-adapt. Heck, Leonidas (the poster above me) runs 1/2 marathons on a regular basis and eats for optimum ketosis. I have no problems doing a sub-hour 40km time trial on a bicycle and do some other pretty intense exercise.