What contractions feel like?

I know it must sound stupid but, what do contractions feel like? Is it like period cramps? That's what I know or that at least they start as period cramps. I am almost 15 weeks now and from time to time I do have period like cramps, they are very mild and they usually last 30 seconds or so. Does this mean I'm having contractions? My doctor told me that whenever I feel period cramps to take an antispasmodic pill but they basically last seconds and there is no time for any pill