For your creatinine level, do you mean 1.3 rather than 0.3?
Regarding the cause, it would be helpful to have more information like urinary protein numbers, ultrasound findings etc.
However, Lithium can be quite harmful to the kidney. It is important to ensure levels of the drug are adequately measured but even then it can cause kidney toxicity. It is more likely to cause toxicity the longer you have been on it.
I suggest you talk to the prescriber of this medication about your concerns. Lithium is an excellent drug for certain disorders, however, it definitely has a down side as well. Please note that I cannot advise you change or stop your medications as this is beyond the scope of this forum. So I am speaking in generality only. Please do not change any medications without speaking to your doctor first.
Thank-you for your question,
Dr. Jordan Weinstein