I am feeling weaker after the 4th week
You might not be eating enough calories per day, or maybe not enough protein each day, to actually build muscle. Try eating a small serving of protein just before bed. If you do supplements, a collagen supplement just before bed is excellent.
Otherwise, it could be that you aren't giving yourself enough time between similar workouts to fully recover, so you are just breaking down muscle without giving it time to rebuild. Or it could be a combination of both.
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