Build Alpha Female - it reduces disease.You're saying nothing I don't know already.
You've made a lot of changes to the diseases, which are fine, but this one just isn't. Getting to those techs will take you over a hundred turns on the slowest speed, while your building speed is slowed down to a crawl. It makes no sense from a gaming perspective to just basically ruin nigthmare for almost all of the civilizations. I had to pick a happiness boost civ to have a normal game.
You can fix it by raising the common cold to hit at city size 2 or not have it hit from the start of the game. Or remove the unhappiness from it.
Also, just because the "common" cold is common today, it's actually over 200 different viruses that cause it - and it wouldn't have been common at all 200.000 years ago.
One unhappiness shouldn't be worse than starting with only one tile.
Language takes only 23 turns to research on Eternity.