All contributions made to the HSA while you were not under HDHP coverage are excess contributions.
It was OK to keep the HSA after you lost the HDHP coverage and even pay for medical expenses from it, but you cannot contribute to your HSA until you regain HDHP coverage.
First, stop contributing to your HSA until you have HDHP coverage again (exclusive coverage, that is, not shared with another employer-sponsored plan).
Second, contact your HSA administrator and ask for the return of excess contributions (the $150). They should send you a check for that amount.
Third, in TurboTax, enter the $150 as a personal contribution, but also indicate that you had "none" for HDHP coverage. This will causes the $150 to be excess contributions. However, unlike for most taxpayers, since the $150 was personally contributed by you and not through an employer, it will not be added back to your income (in case you have been reading other AnswerXchange posts on the same subject) - rather, it will simply not be reported on line 25 of the 1040.
Fourth, if you made any payments for medical expenses using this $150, (as opposed to money contributed legally n 2016), then you must contact the HSA administrator to report "mistaken distributions" and ask (nicely) if you can pay them back. They will ask you for a signed form and a check for that amount.
