Cannot handle alcohol anymore at age 38... Anyone?

I like the taste and the effect of a few beers or wines here and then. Especially in a social setting.. Nothing special, I haven't drunk large amounts for a long time.

But over the last few years I have noticed that I can't handle even 2 to 4 beers anymore. And I'm only 38.

What Happens: A few hours after drinking and when the 'drunken' effect begins to wear off, it is replaced by:

• A restless, nervous feeling in the lower abdomen.
• Fast heart rate, sometimes with some 'skipped beats' here and there (PVC / PAC)
• Impossible to fall asleep because of the above
• Heartburn and 'gas' in the intestines
• When I do finally fall asleep, I sleep very lightly and wake up a lot

Of course, 2-4 beers don't really leave me with a hangover the next day but it's more just the night that sucks hard. And all that from just a few drinks. I have the same effect with wine, just a bit less gassy.

What could be the reason that I 'already' have such a bad time with alcohol? Anyone here who can recognize this?