Nausea is very, very common in some people when they start taking levothyroxine (T4) as is tiredness.
The addition of levo will temporarily make you MORE hypothyroid. Your pituitary has detected more T4 in your blood stream so has decided that you you have enough. However, in reality the levo will not become usable in the body for about 6 weeks. Leaving you a little more hypo than before.
What you are experiencing in all likelihood are more hypothyroid symptoms of which nausea and tiredness are just two of them. You may find yourself with aching muscles or feeling colder too. The staying in bed I can absolutely relate to and still do it now if I've over done it!
Before every dose increase I have ended up back in bed again.
It's very easy to jump to conclusions i.e. I must be allergic, the medication doesn't suit me...
I had exactly the same nausea as did a number of my friends. It will go as your body adjusts to its new method of T4 delivery.
My advice even though I'm not medically qualified is to stick with it and ride it out. Hormones are strong. When re introducing one to your body that it has been struggling to produce, there will be side effects. But they go. Be patient.
Some women get nausea and tiredness when first going on the contraceptive pill. But it goes. They are not allergic to it or the fillers. Their bodies are adjusting.
You could always take half a tablet (12.5 mcgs) for a week or so so that it's less of a shock to your system and them maybe alternate 12.5mcgs with 25mcgs and build towards 25mcgs every day.
I have had to do tiny increases all the way. 25mcgs - 37.5 mcgs- 50mcgs etc.
I was just very sensitive. Now I take 125 mcgs levo plus some T3 too. Some of us are just more sensitive to the introduction of levo levothyroxine and the subsequent dose increases.
You will no doubt have more blood tests in 6/8 weeks and may need a dose increase.
Why not try taking 12.5 mcgs every day for a week or so and then gradually increasing. It may be kinder to your body. But please don't be worry. It's early days and you will get there.
Hope this helps.