A.M. (or a.m.) is the abbreviation for ante meridiem, or before midday. P.M. (or p.m.) is the abbreviation for post meridiem, or after midday.
When we say we wake up at 7 a.m., we are saying that we wake up at the seventh hour of the day before noon. When we say we leave work at 5 p.m., we are saying that we leave work at the fifth hour after noon.
A.M. means morning; p.m. means afternoon or evening. It is redundant to say, for example, “I wake up at 7 a.m. in the morning.” What you’ve said is, “I wake up at 7 in the morning in the morning.” Say succinctly, “I wake up at 7 a.m.” or “I wake up at 7 in the morning.” Choose whichever you like, but do not use both in the same sentence.