TL;DR: To be honest, I don't see anything too suspicious about it. Remember that voting is highly subjective. Reasons why it's probably normal and why you shouldn't worry:
- The votes occurred on different dates, sometimes days apart from each other.
- You asked a lot of questions (over 170). You will probably have to live with the fact that you might receive the occasional downvote.
- The reputation loss is marginal. It takes three downvotes (-6) for every upvote (+5) for you to actually lose reputation.
- You haven't given an answer yet – if you have something useful you want to share or anything you can help with, a good answer will get you 10 points per upvote :)
- Finally: If there really was one user being hostile against your account, you would have received much more sequential downvotes
To help you understand though, let's take a closer look at those questions. Please don't take it personally, I am just trying to explain why it's probably not as suspicious as you might think.
Why have you received downvotes on those? Well, ever since voting on questions became "free" for the user casting the vote (i.e. by not losing any reputation), it became easy to downvote a question.
One of the reasons for doing so (it says so in the downvote button's caption):
"This question does not show research effort".
... which can be argued is the case in some of these questions. Note that I did not downvote any of your questions, but other users might think they fall under that category. Also, take a look at the How to Ask guide:
If you ask a vague question, you’ll get a vague answer.
... and of course (emphasis mine)
Have you thoroughly searched for an answer before asking your question? Sharing your research helps everyone. Tell us what you found and why it didn’t meet your needs. This demonstrates that you’ve taken the time to try to help yourself, it saves us from reiterating obvious answers
... and, last but not least, from the FAQ:
You should only ask practical, answerable questions based on actual problems that you face
To summarize, if a user reading one of these questions thought they might not meet the quality standards or guidelines of the FAQ, you'll get a downvote. It happens.
Now let's see the other two you've mentioned:
For those, it's not that obvious anymore why somebody would downvote those. In fact, I upvoted your second question because it's a valid and practical one, based on an actual problem, and it might also be useful to others. The other one, well, you will have to live with that.
I believe it has happened to all of us. For example, on this question I got downvotes on both the question and my own answer – I still haven't figured out why. But it's nothing to worry about.
Hope that helps!