The bitter taste in beer comes from hops - and it can be quite ferocious at the start, but will tend to mellow with conditioning. It's possible that you have extracted tannins during your mashing process through temperatures being too high, or by your mash pH not being acidic enough (water being very hard?)
When you say 'tastes acidic' - does it remind you of chewing a dry teabag? If so, that's tannins, and it's not really going to go away.