I definitely don't want to lose weight, if anything I prefer to gain weight. I just like this idea of eating "clean".
Well, if you don't want to lose weight (to the point of wanting to gain it), eating paleo (or arbitrarily restricting the foods you "can" eat) is a bad idea: the less food you consider available and fit for consumption, the more you will end up having to skip meals when out and about, and that usually causes your overall calorie consumption and weight to decrease.
Also, what exactly is "unclean" about grains, any more than any other food?
If you want to go back to eating what your "ancestors" did, you'll be down to the only foods available to paleolithic
European nomads (I'm assuming you are white). So, in addition to grains and corn, you'll also need to forget about tomatoes, potatoes, broccoli, most spices, peanuts and a great deal of fruits (not a complete list, just some examples). And if you are really striving for authenticity, then you can't eat ANY fruits or vegetables from the grocery store, because they have all been cultivated AFTER humans settled and learned agriculture, and have little resemblance in terms of nutritional value to the wild plants that hunters and gatherers might have chanced upon. Similarly, the meat will come from domesticated animals, which have been bred and raised to be much fatter than their wild counterparts. So, really, even assuming that the point of a "paleo" diet isn't rooted in a naturalistic fallacy (which it totally is), any attempt at consistently following the principles it sets out will basically necessitate that you become a modern-day hunter-gatherer in Europe or, possibly Africa, depending on how far back you want to go, and, well, assuming you can logistically pull it off, good luck not outright starving.
Eggs should be fair game though: I doubt any gatherer ever passed up a chance to raid a nest they chanced on, after all, starvation is the mother of not being picky about where you get your food
