Why has my hair stopped growing, is there anything I can do?

You may not be seeing any growth due to a condition known as Central Cicatricial Centrifugal Alopecia (CCCA). This condition of scarring hair loss is a result of follicular inflammation due to repeated use of relaxers. The chemicals sealed into the hair during these treatments, as well as the heat applied, can damage and weaken the hair shaft.  However, even if the heat combined with the harsh chemicals contained in the Brazilian Blowout treatment were to penetrate the scalp, it should not typically slow your hair's growth rate--rather, it would cause breakage. 
Refraining from such harsh treatments in the future may help with the overall health of your hair. Consult with a dermatologist near you to discuss your hair concerns and to rule out factors that could contribute to hair loss. 
In the meantime, I have provided a link to learn more about CCCA below. 

Thank you for your question. The damage caused by the hair straightener would have only damaged the visible hair shafts and not the actual hair follicles down under the skin of the scalp. There can be a number of reasons why the hair growth has slowed and there are different treatment options depending on the cause. Consultation with a hair loss expert is recommended. Best wishes

This needs an in-person evaluation. I suggest seeing a hair loss expert now to evaluate and go over your condition and provide you information about your best treatment options. There are great non-invasive options like prp/progesterone and/or hair transplantation. See an expert. Best, Dr. Emer

There are many reasons why hair won’t properly  grow. You require a comprehensive evaluation, blood tests and possibly a biopsy.  Once you and your doctor fully understand the reasons for your hair loss, you can discuss treatments. Until then, it is not possible to suggest a treatment.

Any damage to the hair shafts that occurred from the Brazilian hair straightening treatments should have grown out by now.  Are you noticing any hair shedding? Are there any bald or thinning zones on your scalp? I recommend an in-person consultation with a hair transplant specialist for a detailed scalp exam to determine why your hair is not growing long.

You should seek out an expert in the field of hair. Many dermatologists offer analysis. The quesiton is what type of damage was done when you had the treatment 4 years ago