I've only tried IPAS once, but when I can regularly drink 6 beers without feeling any type of alcohol in my system, it only took one and a half pints for me to feel the alcohol kicking in when drinking the IPA. I just know what it stands for but I have 0 knowledge about them, are they beers? how are they much stronger than regular beers?
Answer to the easiest part of the question: Yes, IPAs (India Pale Ales) are beers.
Unfortunately, there isn't a clear and concise answer to the rest of you question.
Let's assume, for the sake of argument, that by "regular beer", you mean Budweiser. Budweiser sits at 5% ABV. IPAs are often in the 5-7% ABV range, so let's call an "average" IPA 6%. You will feel the alcohol substantially more quickly in the 6% IPA than in the 5% Budweiser.
Lifehacker has a nice article that explains this phenomenon well, but it boils down to the rate at which your body can process alcohol. Suppose that 1% ABV corresponded to 1 "alcohol unit." If, for example, your body could process 4.5 alcohol units/hour, after 6 pints of a 5% ABV beer (1/hr), you'd have 3 alcohol units left in your body [(5.0-4.5)*6]. However, you'd reach the same mark after only 2 beers (1/hr) of a 6% ABV beer [(6-4.5)*2].
TL;DR Version: It probably has to do with the beer's ABV you were drinking.
Side note: There is a lot of variability in strength within any given style. If you like IPAs, you should check out Session IPAs - They are IPAs designed to be lower in ABV than the average IPA, so you can drink more of them in a drinking "session." For a list of the top Session IPAs and more information on the style, check out Ratebeer's Session IPA page.
An IPA style beer has an ABV from 6% on the low end to 10% on the high end, although the higher alcohol ones are labeled as Double IPA of Imperial.
That is probably more substantial than "regular" beer, however that is defined.
Another thing to consider is the body of an IPA. It will tend to be more malty and thicker than say a Budweiser and that will also affect how you feel.
For a variety of reasons, IPA's are generally brewed with higher specific gravities, resulting in a higher (on average) alcohol content by volume.
Without getting too technical, just as others have stated the alcohol content will vary from a traditional run of the mill beer like Budweiser vs something craft like an ipa. The ipa tends to run a little higher in alcohol by volume than Budweiser or similar brands. For example I can down 4-5 modelos Negra without feeling took buzzed but this year I tried pumpkinator and it only too 2 to get me buzzed the ABV is 10% for the pumpkinator vs 5.4% for the modelo