Before further discussion, please tell us the dosage of Synthroid and the NP Thyroid that you switched to. Also, how long on NP Thyroid? Also, did you take your NP Thyroid in the morning g=before the blood draw for those tests? If so, how long after was the blood draw? Do you have any other symptoms?
I like it that your doctor is not concerned about TSH when a patient is taking thyroid med. I am a bit concerned that the doctor was happy with your Free T4 level at only 24% of its range, which is a bit low for many people. You should also always be tested for Free T3 every time you go in for tests. Your thyroid status is related to the level of TISSUE T3 EFFECT, so knowledge of Free T3 level is important. Thyroid medication should be adjusted as needed to relieve hypothyroid symptoms, not based on blood test results alone. Since you are taking NP Thyroid, your Free T3 would be expected to be higher in range than FT4, but you need to know it.
In addition to getting your FT4 and FT3 levels adjusted as needed to relieve symptoms you also need to test and supplement as needed, Vitamin D, B12 and ferritin. Vitamin D should be at least 50 ng/mL, B12 in the upper part of its range, and ferritin should be at least 100. One other thing is that blood test results can be falsely high if you have the blood draw too soon after your dosage of thyroid med. So it is recommended by the ATA/AACE that medication should be delayed until after the blood draw.