The tense form in the sentence "I have been waiting for sometime now" is the present perfect progressive tense.
The present perfect tense is formed using "have/has" + past participle of the verb, and the present perfect progressive tense is formed using "have/has been" + present participle of the verb.
In this sentence, "have been waiting" is the present perfect progressive tense of the verb "wait." It indicates that the waiting started in the past, is continuing in the present, and may continue into the future.