What causes a hen to lay months earlier then she should?

[Mimity85]

I have a Plymouth rock who is 5 months and about 3 weeks old,
I was told it should take her 40 weeks to lay however today she has laid her first egg and it didn't seem like the easiest thing for her to do.

She was in and our of the hen house all day, and then as the day progressed so did the volume of her voice, then half an hour before she laid the egg she made the loudest noises I have ever heard a chicken make, like she was distressed and in pain.
So at this point I started calling vets and they were concerned she might be egg bound.

After half an hour in the coop with complete silence she finally laid a little egg, afterwards her combs were quite light in color, light pink and some parts even lighter, so I gave her some water then she made more very loud distressed noises. After a while she did come out of the coop and start picking at some scratch and had some fresh water I laid out for them.

However I am a worrier so wondering why she would lay so early? Have I done something wrong? Can she possibly be a distressed each time as she is in pain as she isn't fully developed? Don't know alot about chickens, please help!

 

[ShockValue]

Who ever told you that they won't lay until 40 weeks was misinformed. 20-24 weeks is pretty average.

The loud noises you are hearing is affectionately called the "egg song" and is totally normal.

 

[Mimity85]

Thank you!

She is usually such a quiet and docile bird that to hear her volume increase so much was worrying, is there anything I can do to make it easier for her? Include something in her diet?

 

[ShockValue]

Now that she's laying, make sure she has calcium in her diet. Either by offering oyster shell or layer feed, or both. They're smart enough to only take what they need.

 

[Mimity85]

Okay, as after she laid her egg her comb and wattle went quite light pink and white in some spots? Should I get some electrolytes or something?

 

[aart]

They can get pretty goofy when they start laying, it can take up to a month or so before they get it all figured out and settle down.
Comb color can change with blood flow, redder when excited, paler when calm. Purple combs can be a sign of heart problems/bad circulation.

Her paler comb is probably nothing to be concerned about unless she is otherwise acting unhealthy, not eating, drinking, funky poops or isolating/lethargic.
Just keep an eye on her and try not to stress too much.......chickens have a plethora of odd behaviors and it's only with experience that you'll begin to recognize what's normal and what's a need for concern.

ETA: Ditto on the 40 weeks being misinformation. Enjoy your eggs!!