Yes, that's not normal procedure, normally you start on low dose and work up with retests every 6-8 weeks as can be a shock to your system otherwise but also because it takes that long to see the full effect of a dose. Most people are started on 25-50 mcg and then worked upwards in increments of 25 until levels are good. Giving you 150 at once may even make you hyper after a while so not sure who he's getting his information from.
I think maybe you need to show him the following NICE guidelines which they should be adhering too which state:
Initiation and titration
The dose of levothyroxine (LT4) should be individualized on the basis of clinical and biochemical (thyroid function tests) response. Treatment must be monitored regularly to determine an adequate dose and to avoid both under-treatment and over-treatment.
The initial recommended dose is:
For most people: 50–100 micrograms once daily, preferably taken at least 30 minutes before breakfast, caffeine-containing liquids (such as coffee or tea), or other drugs.
This should be adjusted in increments of 25–50 micrograms every 3–4 weeks according to response. The usual maintenance dose is 100–200 micrograms once daily.
For people aged over 50 years and people with cardiac disease or severe hypothyroidism: 25 micrograms once daily, adjusted in increments of 25 micrograms every 4 weeks according to response.
Once a stable thyroid-stimulating hormone (TSH) level is achieved and an adequate dose determined, arrange follow up to check thyroid function tests (TFTs) at 4–6 months and then annually.
You can print off the full details on this link: