Alliteration is a feature of this sonnet, and can be found in the second line, in the words "pleasure of my pain." This is a literary term that is used elsewhere in this poem and you might like to look for it yourself, as it is one of the easiest literary terms to identify.
The poem also contains various examples of powerful imagery, such as in the following line:
I sought fit words to paint the blackest face of woe...
Here, the speaker is talking about trying to write his poem to his beloved to let her know about the impact of his love on him. "To paint" in this quote acts as a metaphor because he is comparing the process of writing and describing his lovestruck manner to painting a picture of what he looks like as he suffers from his passion.
Another metaphor is used just after to compare reading the poetry of others for inspiration to a shower of rain:
Oft turning others' leaves to see if thence would flow
Some fresh and fruitful showers upon my sun-burned brain.
Here, the speaker presents his own brain as being "sun-burned" and in need of the "fresh and fruitful showers" (another example of alliteration) that the inspiration of reading the poetry of others could give him.
There are a few literary terms, and I hope you are now able to go back and analyse the rest of the poem yourself and find some more examples. Good luck!