My doctor told me to get 20-30 compression stocking and the place where i got them they gave me 18 mmhg i been wearing them do you think that's ok?

Speak to your: Doctor, many surgical supply stores will will get you those stockings and measure you to your size , jobst etc companies will supply.

Compression: Something is better than nothing. You should ask your physician if the lower compression will be adequate or not for your condition.

Depends on Condition: I always tell my vein patients that some compression is better than no compression, unless there is some contraindication such as peripheral artery disease. For mild swelling or mild venous disease are likely OK if they are fitted properly for your leg. But if you have significant venous disease in your legs or lymphedema, you would needed higher level of compression which needs a prescription.