Are there any side effects of overdosing on progesterone cream?

Not really. First of all, it is very hard to overdose on the cream and secondly Progesterone is very bening. However, if one uses it inapropriately in terms of timing it can alter cycles and make timing very confusing.
A few... Excessive Progesterone can cause sleepiness and acne. Moreover, if converts to other hormones in the body, can cause oily skin, irritability, insomnia, headaches, breast tenderness, fluid retention, etc. When used at correct doses, it treats all of the above symptoms. Not everyone tolerates progesterone, even at very low doses, and these are usually folks with severe adrenal insufficiency.