What causes genes to mutate/activate?

Not sure this is the right forum, but it's the closest I could find.

22 year old female here, adopted at birth, unknown genes.

Some weird things have been happening in 2012. My body has started responding differently to things, and I'm not really sure why.

For example, a couple of weeks ago I went to the beach. Ordinarily on such trips, I get sunburn unless I apply sunscreen at least 3-4 times over the course of the day, and even then, I've gotten sun poisoning and heat rash in some cases.

This time, I was down for about five and a half days. I definitely didn't apply sunscreen that much; a maximum of twice per day. I know the signs when I need to start being paranoid about sunscreen: I turn a nice pink color, but it doesn't hurt; I just look like I have good color to my skin. This did happen on the second day, but then it went away by the end of the third. I applied sunscreen thereafter only once, right before I went out on the beach, each day.

Now, if this were as little as two years ago and I had done this, I would have been burned, blistering, and peeling. Instead, I turned a pleasant light tan.

I have NEVER IN MY LIFE TANNED. EVER. Even when I was fully-sunscreened, if I got sun, it wasn't tan; it was PINK. (Not the angry red of sunburns, mind you: a pink that didn't itch or hurt)

There have been a couple of other unusual things going on lately. I developed Plantar Fasciatis due to bad shoes, I have been getting allergy shots (because I have horrible allergies), and I've started living with cats, something I've never done for allergy reasons, but surprisingly even before the allergy shots, I seemed to be less allergic to cats.

I know genes can be "activated" by things such as viruses (my friend has a gene that activates in response to influenza, basically giving her relatives multiple food allergies if they contract influenza), but are there other things? What could make a tanning (as opposed to sunburn) gene activate in me at twenty-two years old that has previously been dormant?

Curious to see if anyone has any idea about this.