I too am sorry to hear of your loss. I went through the same and even though it was 30 years ago, I can still remember how raw it all felt.
To reinforce what the others have already said, you can feel really rough when you drop a load of carbs - it's called carb flu - your body needs time to adjust to the totally different regime it is now under - it does get better, I promise. I can remember standing in the shower on the morning of about day 6 of my lower carbing regime and thinking that I'd made a mistake as I felt so bloody awful.
One tip I was given here that did help, was to ensure that you get enough salt - I found drinking a hot Oxo cube drink really helped how I felt. It takes a few days adjusting, but it will be worth it long-term, I promise.
Another thing to consider is that as your blood sugar drops with the change in eating regime, your body needs to adjust to that too and that can have an impact on how you feel also. If you can stick it out for a few more days, I'm sure you'll pick up.