。
Even I'm amazed at how forgetful I am.
Literal
Forgetful [nominalizer-の] [dat-に] [topic-は], myself [concessive-ながら] be-taken-aback
Three things worth pointing at. 忘れっぽい uses the suffix ~っぽい, which turns nouns/verb-stems into adjectives meaning 'tending to be X' or 'X-ish' — here 'prone to forgetting'. 自分ながら literally 'being myself' with concessive ながら = 'even though it's me' / 'even I myself'. And 呆れる is stronger than English 'amazed' — it's being taken aback to the point of dismay, often with a note of exasperation.