After being on tobradex for three weeks, the inflammation in my right eye is improved but not gone. the doctors says it's irritation from dry eyes. she gave me a milder steroid (i don't know which one yet). is it safe to use for another week?

Some people (rarely) will get a steroid induced rise in eye pressure if they use any type of steroid, usually after 1-2 weeks of use. If the eye pressure was normal after 3 weeks it should be safe to use for another week (especially if a milder steroid). Cataract is another complication of steroid use, but usually much longer term than 3-4 weeks.