"I don't know where to start"

I am now 18 week pregnant and considering changing hospital. There are several problems with the antenatal care I am receiving, I will mention 3 issues: 1) First of all, it is impossible to get through to antenatal bookings (020 7188 8002): after calling them around 40 times over 3 weeks to arrange an "urgent" appointment and leaving 3 voicemails with my details, I finally managed to schedule an appointment thanks to the intervention of the complaints department. 2) My 12-week scan was an appalling experience. Having had a miscarriage before and bleeding plus other problems at the beginning of this pregnancy, my husband and I were looking forward to finally breathing a sigh of relief. After the scan, performed by a sonographer who lacked empathy, they sent us to the waiting room again saying that my blood test results were not back and that they would call us back in as soon as they got the full picture. We saw people coming and going and after around an hour of waiting I realised that I was the only woman left in the unit and most personnel had left for lunch. I started walking around and saw the sonographer wearing their coat and going towards the lifts. I ran after them and told them they hadn't given my results yet. They rudely replied they had not performed my scan. It was only when I did not let them take the lift that they agreed to check. We went back to the scan room and they looked for my results. When they finally found them (with no word of excuse) they said that in any case all was good and I needed not worry (!). At that point I looked at the computer screen and I realised that my details are all wrong...they must have entered the details of another woman under my name! 3) I have been having thyroid problems since the beginning of the pregnancy, which were diagnosed by chance by a private gynaecologist. I asked the midwife at my booking appointment to add specific blood tests to the routine ones. They replied they would only do that after I had seen the obstetrician, the first appointment available being...1 month later! When I finally saw the obstetrician (at 14 weeks!) they said I should have had blood tests much earlier, as the baby could have been impacted by the lack of follow-up in the first trimester. They ordered blood tests, and one week later the midwife wrote to me saying that the obstetrician wanted me to reduce the thyroxine I was taking. At that point however I did not trust the care I was receiving anymore and had been to an endocrinologist, who recommended to double the thyroxine. I have since then consulted two more gynaecologists, who both agree that I should double the dose and that the NHS obstetrician is simply utterly wrong. I am lucky I can afford second opinions, otherwise I would have done something potentially very damaging for my baby and myself. How can I trust anyone in this hospital anymore?