Get your test results and ranges and start a new thread putting them in. It is your right under the Data Protection Act 1998 to have a copy of your results a few days after you have asked though you may have to make a more formal request from your GP to get them. So if your GP is difficult start a new thread for advice.
Hair appears like it's not growing if you are under medicated and/or have vitamin and mineral deficiencies. The hair is actually growing but shredding earlier so grows to a shorter length. The fact that it is dry indicates that you have metabolism issues and the likely cause is what is already mentioned.
As you are likely to have thyroid hormone results we can have a look at that first to check you are on enough levo then we can ask you to get your vitamin B12, folate, iron (ferritin and heamoglobin) and vitamin D plus thyroid antibodies tested. It is normally easier though more expensive to do vitamin B12, folate, ferritin, vitamin D and thyroid hormones privately. Then if your ferritin is near or under range get your NHS GP to do a full blood count which includes haemoglobin plus tests for iron deficiency anaemia markers.
While iron levels are normally the main culprit in hair problems people do see problems if their B vitamins and vitamin D aren't optimal.
Just be aware levels for iron and other vitamins optimal for hair growth coincide with those optimal for thyroid condition sufferers on this board, yet most medical doctors believe you just need to be in range to be fine. So it's a waste of time asking or listening to most doctors as they say your levels are good when they aren't. For example a few months ago I told my haemoglobin level was "very good" by a GP but it was too low for me to be a blood donor under NHS blood donation rules!