Having your thyroid checked only requires a simple blood test. You can be breastfeeding - it won't be impacted at all. Thyroid impacts a LOT of things. I discovered my thyroid was off after 3 miscarriages (even though it had been tested after the 2nd one and was deemed 'normal'). After starting meds, I had 3 effortless pregnancies. However, there have been a few times my meds got out of wack (stress, weight, health, age, whatever) and boy it made a HUGE difference - weight, appetite, fatigue, depression, ability to focus and stay on task, etc. What you should be sure your doctor realizes is that the lab's 'normal' range is rather large. Having a level of 4 might make one person feel great but another person might need a level of 2. You really want the level to be as low as possible, so even if it is in the 'normal' range, you might want to insist on trying meds to see if it makes a difference for you. Good luck and feel free to email me if I can help answer any questions. All it is is a simple little pill that you take every morning - I've done it for 12 years now - really not a big deal!