I haven't had it in 2 and a half months but I tell my doctor I have it every month
AT age 18 it's not ok to lie to your doctor. Various under lying medical conditions can cause that and it could even be serious ones. Go back to the doctor and explain to them or get one you are more comfortable with.
No, it's not okay. At your age, that could mean many things, and lying to your doctor isn't going to make any possible health problems go away. Could you be pregnant? It might be a good idea to look into that.
Dont EVER lie to your doctor, You could have a very serious condition and you wouldn't even know. Its a disaster waiting to happen, don't do it. Answer On!