Quick list of thyroid things for you to compare:

Overactive thyroid:
-sudden unexplained weightloss
-increased appetite
-racing heart and/or palpitations
-feeling hot or having flushes
-increased sweating
-difficulty sleeping
-hair loss or thinning hair
-feeling anxious, twitchy or like you can't relax properly
-inability to "switch off" mind at night, thoughts racing etc.
-feeling physically jumpy and having overactive reflexes (like touching hot but not burning hot objects results in strong reflex withdrawal of hand)

Underactive Thyroid:
-Weight gain or inability to lose weight
-decreased appetite
-constant dragging tiredness which sleep doesn't alleviate
-slow resting pulse (take it first thing in the morning before you get out of bed, unless you're an athlete you'll be around 58-70 beats a minute, i was 38bpm when illest!)
-feeling cold even when others are warm, having cold extremities which are hard to war up even with hot water bottles/heat packs etc.
-not sweating
-hair loss, loss of eyebrows (especially outer 3rd)
-dry skin, and/or thickening skin
-puffy eyes, facial swelling
-joint pain (hands, hips, knees especially)
-muscle pain (thighs and back especially)
-slow healing of injuries (minor or major)
-easy bruising from slight knocks
-"foggy" mind - hard to thin, poor memory, change in alertness
-slow reflexes
-emotional depression - "blah" feeling of indifference without a root cause one can pinpoint

Both underactive and overactive thyroid
-swelling of the neck (enlarged thyroid gland - goiter), difficulty swallowing, feeling of "lump" in neck or aches or bruised feeling around the voicebox.

If you have 3 or more from either list (women often have overactive THEN underactive thyroids, so if you've had things of both lists recently it would still indicate a problem, they don't cancel one another out!) then a blood test is advisable.