sounds similar to what i have, but i have a very unusual heart racing/pulpatation along with the shortness of breath, and it only happens for about a minute each time.

Mine was put down to anxiety, even though im not anxious about anything (that i know of)

but just get it checked out with ur doc, cause as you said, if ur only 22 weeks, heres to hoping it wont get worst :/

all the best, hope it eases a little soon xx